I have noticed, after playing through the campaign several times, that a lot of maps for one battle are re-used in another battle. Sometimes this makes perfect sense - namely if in real life the two battles happened at the same place (example - 1st Bull Run is almost entirely contained within 2nd Bull Run, and the southern part of Cold Harbor overlaps entirely with Gaines' Mill). But for several other battles the only reason would be that the developers did not want to waste effort making new maps when their old ones are perfectly reusable. I don't mind at all - it means that you can learn strategies in one scenario and apply them to another scenario, plus the simple fact of approaching an objective from a different direction leads to new tactical challenges.
That said, I think it would be helpful if we had a List, in one place, of what battles (Grand and Minor) are fought on the same terrain. My post will include every battle that I can remember, but Please Feel Free to update and add any more battles that you think of (and attach the right names to some of the minor battles).
In order of Grand Battles:
1st Bull Run is roughly the eastern half of 2nd Bull Run (extending a bit east of the Stone Bridge), but there are at least two occurrences beyond that. The southwestern region of 2nd Bull Run, at the town of Groveton, is re-purposed as Newport News (Confederate minor Battle in 1st Bull Run campaign) - you defend from the south as Union attacks from North, NW, and East. The western edge of the map, crossing over the creek, overlaps with the Confederate minor battle of Weapons Factory (Harper's Ferry) in the Antietam Campaign.
Shiloh gets re-used once confirmed. It's southeast portion, from the river to the southeastern 2 objectives (Camps), is also the second-to-last minor battle of the entire Union Campaign - forgot the name (something-Bluff) - where as the Union you attack west and north from the river into Confederate Entrenchments. I *think*, but have not confirmed, that the northeastern area around Pittsburgh Landing (final objective) is also the first of 2 minor battles in the Union Chancellorsville campaign, where you attack Longstreet and try to destroy 3 heavy batteries in a fort along the river bank.
Gaines' Mill, besides overlapping Cold Harbor, also has its western portion re-used (the lake by the dam). It is the Union minor battle River Crossing (Shiloh Campaign), where the Union attacks from the west, across the first stream, to take 2 hills. [Cold Harbor has a bunch of its own overlaps; see further down this list].
Malvern Hill has its map show up in at least four minor battles. The northern portion, where the stream is crossed by 2 bridges and 2 fords, becomes the Confederate minor battle of Cross Keys (Gaines' Mill Campaign), where you defend the woods west of the stream against Union attacks from the east. The far southeast part of the battlefield (East Malvern Hill Objective) is used Twice. Once is the immediate next Confederate minor battle - Port Republic: you attack into the woods from the northwest, and then defend against Union reinforcements arriving from the northeast across the stream. That same area also becomes a Union minor battle - the 1st of 2 in the Antietam Campaign (forgot the name - one of the 2 Gaps) - where you attack from the southeast uphill into the woods to take the little house at the corner where the field begins. Finally, the West Malvern Hill objective is the stage for the Union minor battle of Bayou Forche [sic?] in the Chickamauga campaign - you can flank the position to the north by the upper bridge, or by the part of your force arriving from the southeast.
A set of minor battles use exactly the same maps - the very first Union minor battle (Distress Call) and a Confederate minor battle in the 2nd Bull Run campaign (Manassas Depot) use the same map - the one with 2 supply depots in the western portion of a big field surrounded by woods, that you have to hold/attack.
For a second set: the Confederate minor battle of Corinth (Fredericksburg campaign) is the area around the south-central objective marker of the Union minor battle of Jonesboro/Georgia Railroad (Richmond campaign).
The town of Sharpsburg (from Antietam) is apparently also the town of Winchester, as it and the woods to its west and northwest is the focal point of 2 minor battles (1st Winchester, Confederate minor battle in Gaines' Mill campaign, and 2nd Winchester, Union minor battle in Gettysburg campaign). Additionally, the far northwest corner of the map overlaps with the Union minor battle of (Siege of) Suffolk from the Chancellorsville Campaign.
(I have not yet found any Re-uses for Fredericksburg).
Stone's River shows up again a few times. The area around the final objective markers was seen once before by the Confederates as Stay Alert, a minor battle in the Shiloh Campaign, where you defend the area against Union attacks from the western half of the compass. The area around the middle objective markers (phase 2) becomes Hardin Pike, one of the last Confederate minor battles in the Washington campaign, except the Union now has Fortifications up the Wazoo. The southwestern portion of the map (the open area west of the initial objective markers) is used in another Confederate minor battle - Prairie Grove - in the Fredericksburg campaign, where you defend against Union attacks coming from the north.
The heavy woods at Chancellorsville lend themselves well to a few minor battles. A rectangle formed from the Chancellor House (main objective) and going southeast becomes the Union minor battle of Iuka (Fredericksburg Campaign) where you attack from the south and enjoy overrunning outnumbered ill-equipped Rebels. Starting from the same corner and make the rectangle a lot larger, and you get Brock Road, a Union minor battle in the Cold Harbor campaign. The far south-western region of the map (not usually in play unless something *wild* happens on May 2nd) meanwhile is the Confederate minor battle of Saunder's Field that also happens in the Wilderness (Cold Harbor campaign). [While both of these battles *could* be made to overlap as they did in real life, here the game developers messed up. The Union minor battle should be where the Confederate one is, and the Confederate one should be about half-way up the left side of the map rather than at the corner.] Meanwhile, the northwest quadrant (over which the Confederates attack on Day 2) overlaps with the southern half of the Confederate minor battle of [Siege of] Jackson from the Chickamauga campaign, with the main east-west road from Chancellorsville being the southern border of the latter's map.
Gettysburg's iconic map still manages to show up in a few other places. The western part of Day 3's map, from the very fringe of Cemetery Hill and Ridge down to in line with the Peach Orchard, and heading west, overlaps as the "eastern" [really northern, the map is rotated] half of the Confederates' minor battle of Laurel Hill from the Cold Harbor campaign. Meanwhile Culp's Hill is the same objective as the West Redoubt objective from Hall's Ferry Road (Vicksburg), a Confederate minor battle in the Washington campaign. Going south from there, sticking just east of the main objective markers (in what was IRL the Union behind-the-lines area), you then reach the 1st Franklin battlefield (Confederate minor battle from Chancellorsville Campaign).
Chickamauga shows up in at least 2 other places. First, the area from the middle 2 objective markers and heading west into the wooded ridge, is the *other* Union minor battle in the Antietam Campaign (the -other- Gap), where you attack from the east across the small stream to seize the heights. Second, the bridge crossing almost forgotten on Day 1 (since it uses Wilder's brigade, which is not your own), happened as another Confederate minor battle, Blackwater Heights, from the Chancellorsville campaign.
Cold Harbor is a huge map that shares terrain with a record *6* (at least) other engagements (besides, of course, Gaines' Mill, overlapping from real life as previously mentioned). The far northeastern portion of the map (comes into play on Day 2 as the Confederate Left Flank objective) is right on top of Salem Church, the "minor battle" (in quotes because it is a mandatory one) that is a part of the Grand Battle of Chancellorsville. Proceeding southwest from there, the open area northwest of the next objective marker (Bethesda Church) is the map for the Confederate minor battle of Ambush Convoy from the Shiloh Campaign. From there, going due south and stretching to the eastern edge of the map gives us a bunch more minor battles where the stream comes in from the east. North to South, the first is Thoroughfare Gap, Union minor battle from 2nd Bull Run, where you hold a wooded area northeast of the stream and the Confederates attack from the Southwest. Extending this map a bit south gives you the a Confederate minor battle Cedar Mountain (also from the 2nd Bull Run campaign), with exactly the same position [but not actually the same position in real life] so now you (Confederate) are the attacker. Then this map in turn overlaps as the northern part of a later Confederate minor battle (Chantilly, from the Antietam campaign), where you defend 2 wooded areas against Union assault from the south. Taking us to the south-central area of the Cold Harbor map, at the Old Cold Harbor objective (basically the 1st Day 1 Map), gives almost the exact boundaries of Seven Pines, a Union minor battle from the Gaines' Mill campaign.
Fort Stevens' (the Union mandatory minor battle immediately after Cold Harbor) map is, of course, contained in the map for the Confederate Grand Battle of Washington. But so is the infamous Rio Hill, Confederate minor battle in the Chancellorsville campaign, in about the same place (northwest area of the big map), just sans fortifications.
Meanwhile, the battle of Mansfield (Confederate minor battle in the Cold Harbor campaign) overlaps with the south-central region of the 1st map of the 1st day of the Union Grand Battle of Richmond.