Just wondering if anyone knows, or if a blue can answer this question...

Several titles on GOG have counterparts on the Steam store that have had achievements since release.

Will these achievements be added retroactively to these previously released titles on Galaxy?
Or will they only be available in select future releases?

Only answer we can give is maybe.

I'd bet money on "No". Most achievement stuff is based on events while you're playing the game, there's no "game log" to suggest what you've done.

I could be wrong, not a game developer myself.

Game dependent actually. Sword of the Stars: The Pit does have achievements, and they are stored by the game themselves. Played the GOG version and got some achievements, then got the Steam version as well. Next time I triggered an achievement, Steam client recognized the previous ones as well.

Additionally, Binding of Isaac locally stored the achievements, so one could download a file with the achievements already unlocked, which was used back in 2012 (or was it 2011?) when Steam had achievement hunting for gifts during the Winter Sale.

That's interesting to know. Thanks for this. I wonder how this is protected against some people just copying "achievement" files. I suppose the devs don't really care?

Why would they? It's no different from using cheat codes in single player. As long as you're not trying to alter your ranking in an online game (which shouldn't be possible locally anyways), it really shouldn't matter.

I think the OP is not asking about getting achievements added retroactively for a past playthrough, but just wondering whether games that have achievements on Steam will have the same achievements added to their (already released) GOG versions, so that we'd be able to get them on future playthroughs. Or whether achievements is a service that only games released in the future will benefit from, and not the ones that were already in the catalogue before we got the client.

We can give any answer. I'll give square root of 2 divided by pi.

Depends on the dev. I know with VVVVVV, all the achievement information is stored in an unencrypted plain text file. It was possible to get achievements just by editing a couple of numbers here and there in Notepad.

That's exactly right!

I'm not referring to (would-have-been) earned achievements.
Just whether they will become available to unlock in a future playthrough.

Hadn't realised it could be misinterpreted... thanks :)

I've been wondering that about FEZ and the new Avernum games.

Personally my answer would be 42.