Think of states that were part of either the Union or Confederacy, and it’s natural to envision that, say, the attendees at the Great Reunion from New York were almost all Union veterans and those from Virginia were almost all Confederate veterans. In the official proceedings you can find a table that lists, state by state, how many Union and Confederate veterans attended from each state and you will see that there were in fact small numbers Confederate veterans attending from a Northern state and vice versa, most likely because of post-war migration.
The most balanced Yankee-Rebel mix at Gettysburg in 1913 within a state’s delegation? West Virginia: 562 Union veterans were joined by 563 Confederate veterans. The Rebs win at the buzzer by one!