I own all reinforcements packs as well as back to war here on gog and im pretty sure they're installed, but i cant use any of them in-game for some odd reason.

When i look at the included divisions in any way it says they're locked and when i click on it they send me to the gog.com page for said dlc, even though i own it and they're installed.

Gotta say im not a fan of the new gog galaxy.

EDIT: yea i had to enable them in the installation settings. my bad.

I still blame the new gog galaxy

Yes, Galaxy2 hides this.