I would treat it like one does a check? You have the equivalent of a cancelled check that says you did not make more than $770 for that month, so, if they try to come after you later, it's not like there will be any surprises/need to for them come after you in the first place? You have the amount you made and proof, if they do want it later. Nothing bad can happen with that. Did you take down the 3 SSDI reps's names?