I feel safe that the GB crew will do the right thing and not spoil major plot points in any of those games much like they wouldn't on a regular Bombcast. It would be pretty irresponsible otherwise especially since stories in those games don't need to be talked about in great length and I'd rather hear about how the games play than anything else.
Hm. Realizing that I've now played everything I was worried about other than Assassin's Creed III. While I'd appreciate them avoiding spoilers for that game, I have a feeling two of the three major points in that game have been well and spoiled for me, so I'm not so worried about it.
@Tylea002: I went ahead and threw (edit durr... I wrote through) this together: http://www.giantbomb.com/forums/bombcast/32/2012-goty-bombcast-unofficial-time-stamps-the-thread/572299/#21
I'm hoping the community will help fill it out. I did as much as I was able but really that's not much.