This series contains modules published by Barrataria Games. The modules are not connected thematically and have unique "lettercodes" resembling the codes used on TSR-era adventure modules for D&D products.
According to the cover blurb (below) these modules are written for Basic D&D but are easily converted for use with AD&D.
from the cover blurb:
...for use with all “classic” fantasy roleplaying game rulebooks or sets for Basic-level players and gamemasters. It can be converted for use with “Advanced” fantasy game rules and compatible systems with a minimum of effort.