voodoo47: yes, the detection issue has been fixed in the last GOG update. the GOG version of Thief Gold includes a set of fixes that make sure no critical or major issues are encountered - you can call it TFix light, if you want.
the same set of fixes, plus some more tweaks, is included in the full version of TFix. if you "just want to play the game and have fun", you should go for the full version of TFix (after applying the latest GOG update). if you need to see the game in its original state, including all the flaws (for a retro review, for example), stick with the GOG version, without TFix.
Thank you for your insight, guys. So it sounds like after installing GOG Thief Gold, then the update patch, then Tfix 1.16 from TTLG, I'll be good to go! Glad to hear there is no longer any potentially confusing exe. recognition issue that could hamstring my experience.
As an aside, am I right in understanding that the NewDark component included now in the Tfix patch is responsible for the widescreen resolution/ratio support (engine modernization), and that it is in fact NOT included in the GOG version (higher resolution)?
Irregardless, I'm always thrilled when a dedicated community produces fantastic patches that revitalize classics- particularly when they are compiled in such a convenient all-in-one patch! I'll definitely go with your recommended install order Voodoo47- can't wait!