The Final B should not have any major functional changes but rather fixes, tweaks, and other little things to make it a more polished Final Version. So, saves from the Final A but NOT test (I don't recommend saving Test Version saves for the next part) I would say are fine. I am considering adding part of a scene for Final B but it would not impact saves from A since I would make sure not to include any critical flags/points for the scene but rather just start the scene and get it going. Maybe a good 40 renders to get it rolling as the overall scene is actually in my head at least 150+ maybe 200 renders. But no promises as I just want to see how I feel tomorrow, etc.