The Caverns of Thracia is considered by many to be a classic old school adventure from none other than Paul/Jennell Jaquays. While this might be true the actual maps in the adventure are somewhat confusing. This has been documented in various places and is not something new that is being pointed out. A good clarification of some of the interconnections of the maps can be found here.
I have the original module from back in the days of the Compleat Strategist in Montclair. While going over the adventure in preparation of running this I found the need to revise/update the maps to have a better grasp of the various interconnected levels/rooms/passages. While I do this as a matter of routine when starting any new adventure this proved to be more than just my passing need to re-do the maps in old school blue in this case. You can see some of the areas explored thus far by the group on the map in blue.
Not that radical of a difference but the DM version has some more detail/info than what's shown in the published version. At least the old/original that I have. From what I'm given to understand the maps have been re-done and are much clearer these days in the newer version for sale. The first level map has been posted in more than a few places, so I'm not really giving anything away here.
A good level 1 treatment of the map/adventure can be found here if anyone's interested.