http://www.slitherine.com/forum/viewtopic.php?f=121&t=76489
It was a fix 14 months ago for 1.30, but it wasn't changing the ingame 1.30 tag.

EDIT: It should be yes, as written tiny in bottom of welcoming screen of the game.

So GOG is missing this patch?

I don't think so: at least the gog version is written 1.31 ingame. So it should be the good last one.

There is already version 1.32 but Steam and GoG do not update !
http://www.slitherine.com/forum/viewtopic.php?f=121&t=76489&start=20

For anyone that wants the latest patch for Panzer Corps/Panzer Corps Gold (version 1.32) you need to go here:

forum.slitherine.com/viewtopic.php?f=147&t=106604

The flashback games links are dead (forums are offline probably) but this patch has all the latest fixes (sub attacks etc) and they allow for increased hexes for new mods and campaigns offered at the forums.

Just follow the instructions on the thread. Enjoy!