I have multiple remotes (both for P3A) and one seems to work better than the other. The one that seems to work better belongs to a lost drone. Question is: can I link more than one remote to one AC? Obviously, I don't intend on using both RCs at the same time, so we don't need to go there.

If you need to change RC for your Phantom 3 Adv, you can bind the connection again: power on the drone and the RC that you want to link (keep the original one off), link the drone and RC then it will work. Note that the connection between the drone and the original RC will be terminated when you switch the connection to another RC. If you want to bind the original RC back, do the linking again. And one drone supports one RC, users are not able to link multiple RC at the same time.