BKGaming: Bannerlord is fully updated and is updated nearly the same time as steam as far as non beta updates. Only Steam get's beta updates though.
ChrisGamer300: I see, thank you that's what i have expected from Taleworlds so good that those fears are unfounded.
They weren't unfounded; in the 1.5.x version range, there were several updates which took weeks to arrive on GOG after having arrived on Steam. I think TW has gotten better about this since then, although I don't know how it's been since 1.6.1.
Bannerlord is still missing the mod tools for GOG version as of the time of this post (as the OP's doc says), and I believe multiplayer is nonfunctional as well for GOG customers. I was never able to access
BL's MP even when logged into Galaxy with an up-to-date game version, and I heard other GOG customers say they had the same problem (and never heard this from Steam users).
Taleworlds' GOG-release announcement and GOG's store page both
fail to mention anything about any of these 'downgrades' for the GOG version.
Unfortunately, a prospective buyer is unlikely to see this thread prior to buying (I sure didn't have any way to know about it until accidentally discovering it today while searching for something else), but having this list available here is better than nothing. My thanks to the OP and other contributors.