I think I have found the issue, looks like the UnitInfo files for two Houses also have info about Adventurers. Specifically houses Ghandalla and Phiarlan. Neither of them had the tag. Adding the Code: <PrereqCiv>CIVILIZATION_GRIGORI</PrereqCiv> tag to both the files seems to fix the issue. Something odd happened while I was doing this, however. The first time that I experimented adding the tag to only one of the files (I think it was Phiarlan) a bunch of other new (and useful) info started showing up in the Civilopedia about how Adventurers and many other units like Archmages and Nobles of Houses would add support for various houses when built. Now I can't see any of the support information in the Civilopedia regardless of whether I add or remove those tags from the Unitinfo files from either House. I've tried clearing the cache, starting a new game with the "Houses" option on, everything else I know, and the House support info for units doesn't show up in the Civilopedia. Anyway, at least that fixes the issue with the Adventurer not showing up as a unique unit for the Grigori.