Being "the original Windows edition" I assume that this is "Corpse Party Blood Covered". Is this correct?

For more info on versions: Corpse Party on wikipedia

I don't know? Corpse Party PC & 3DS - Victim’s Memoirs (1/?)

That's correct, this version is Blood Covered, with all the new characters and enhancements.

Ok. Thanks.

What was today's update?

According to the Steam Comunity forum: http://steamcommunity.com/app/251270/discussions/0/1480982971162123765/

So "hardly matters for the [Steam] user" but "literally does not matter at all for the GOG user."

On the plus side, they're making sure the GOG version is in-line with the Steam, which is more than we can say for some developers.

Well, it matters for that incredibly small minority that want to own and play the game on both platforms.
I have met such people before. Those super-rare users would love to unlock achievements on both platforms at once.
The game EXE does support both GOG and Steam, even simultaneously as such now, and yes, the versions have parity.

Edit: Also, actually, for GOG users that isn't completely true. There was one GOG Galaxy addition: Cloud support.
But... the fine folks at GOG have to turn that on before you'll see it working, even though it's in there right now.