When I add a game from a free weekend on Steam, it will stay in my collection on gg.deals even after the free weekend is over and the game is gone from my Steam library.
After the game is gone from my Steam library gg.deals will still say I have it in my collection but if I actually click on the "Owned" button on the game page it will say "Launcher: none" instead of Steam like it usually does. So it seems to remove it from there but still keeps it in my collection "without a store" attached ..