You're right. If the issue could be solved as part of the Geneva Accords, there is no reason that could not be the starting point for the issue in final status talks. At this point, the 'prisoners document' is only a plan for Palestinian unity on issues to be negotiated. And it satisfies all the Quartet criteria and preconditions for moving forward.
U.S. State Dept. condemns 'vicious terrorist attack' that killed Palestinian infant (Haaretz)
from the article: Between prisoners and captives