You already signed off on your percentages, so that's your main input into accepting severance.
You need to check your DD214, which is the document directing seperation pay that finance uses, from their seperation code. Transition office creates the DD214 and has you sign, should be last step in outprocessing. The seperation code won't make any sense to you. Ask them before you sign if you're getting seperation pay, they should be able to yeah or nay, and you'll just have to trust them. If they act like you're crazy, they didn't get the PEB information somehow so you will have to figure out what went FUBAR. Never heard of this happening. They have to check your contracts and if your ETS doesn't match up they won't make a DD214 unless they figure out why, so they'll figure out that its the PEB that authorized the early release. Medical extensions don't come with a contract either, so that throws em for a loop just as much if they don't have the PEB info.
Seperation pay is part of your final paycheck, which should reach you in less than a month after ETS. Exact # of days depends on when your final ETS is compared to their processing cycle. My understanding is 10 days to process the final pay, if that gets to them by the 9th you see pay on the 15th, or if by the 23rd, see it on the 1st.