Yeah, "Cave of the Unkown" seems to be a riff on Zelligar's epithet and the title of B1. So it seems likely that it was meant to be a subtle hint to insert B1 there. Like others in the thread have mentioned, I don't think the geography quite works. My B1 is some miles north of the Keep.
My Cave of the Unknown is a 3 level dungeon with a group of evil clerics rivalling those in the Caves of Chaos on the first level. The second level is a group of undead, with the third level being filled with wererats and thouls. There are connections with both the Caves of Chaos and a 7 layer dungeon underneath the Keep itself (which in turn connects with the Underground Empire of the Troglodytes).