If you are at a level 7 for a while and get raises, then move to a 12, and are unsuccessful, and then go back to a 7. Do you get to go back to where you were in the payband, or back to the bottom of the 7 band? Hope this makes sense.
Article 108, section 6(g) of the CBA covers this. It'll be as if you never left the ATC-7 facility for the entire time you were at the ATC-12 facility, which means that your base pay would go up by whatever presidential or contractual raises you would have received during that period.