You’re right. I got it backwards. The point I was making was that the dual name situation didn’t arise because Gettysburg was a double victory for the Union.
It’s amusing to note that I was reminded of this question while listening to the song “Amtrak Crescent” by Scott Miller & The Commonwealth. The song playfully notes many of the major train stations on the line from New Orleans to DC and comments on the Manassas stop –
you better say Manassas if you say Bull Run
or in Virginia you won’t get along with anyone.
Also, the closest body of water to Gettysburg of any size or significance is the Susquehanna River, but that’s too far away to be useful as a descriptor.