Are the collectibles required for 100% sync in AC3 and 4? I'm not talking about the PSN trophies/ Xbox achievements, I mean the 100% sync in the in game progress tracker.

I'm currently replaying AC4 to try and get the 100% sync, but it seems that I can't replay the Assassination contracts. I've already missed the optional objective for a couple of them. Does this mean that I won't be able to fully sync the game? It seems confusing, cos I looked at the progress tracker and it still says that I 100% the contract(s), even tho I didn't get the optional objective. So does that mean that the optional objective isn't needed to 100 sync them, or does it mean that I can't fully sync the game after missing the optional objectives??