So since Bungee doesn't seem to care, I think I have figured out the problem with the Prophecy Tablets on Mercury. The issue is that at seemingly random times Vance will stop giving new prophecies for the forge. Well it seem that it has do do with the weekly limit and the weekly reset. From what I have gathered, it seems that if there is a prophecy still in your inventory when the weekly reset happens, D2 doesn't reset the count. So if I do 3 LP quest in week "A", collect quest #4 for the week but do not finish it by the weekly reset, week "B" starts me with 3 completed LP quests and an active #4 quest. So when I complete the active quest I carried over from last week, I cannot receive any more in the new week "B", because it counts 4 completed quest. This is the most asinine system yet Bungie, WTH? (It also seems that randomly, if you don't take a new prophecy by Wed. You may not get any more for the week regardless if there is an active quest in your inventory.)