Save Pay FAA to DOD

Im currently making the transition from FAA to DOD and I'm being told by HR and the Org that the DOD doesn't match base pay. I'm currently making $64,816 Base. The new position is offering GS12 Step-1 @ $63,600. Is save pay a policy in writing or is it just a courtesy?

So I found the excerpt below on the pointsixtyfive faq page.

-If entering the FAA from another federal position, your basic pay rate will transfer to the FAA, which will then have the applicable locality pay added to make the new base pay. The same applies leaving the FAA; base pay will transfer over to the closest GS step (rounded up) within the grade you are transferring to, then applicable locality/SSR rates will be added.