If you bought the Collection at any time, you have all the DLC for the first game. There's no way to not have it. All versions of the collection had KA, Druids, Saxons, Artifacts, and Knights.
If you for instance, bought the game standalone and picked up DLC here and there, then yeah, I can understand that being super annoying.
Well, thank you for that, obviously there's no way I found to verify that Artifacts and Knights included and I have no idea how you or anyone else knows what was part of those packs at any particular time, but you claim to and I have no reason to disbelieve you (you can pick Druids and Saxons from the campaign menu, which was the only reason I knew I had those for sure). That's why I was terribly annoyed, hope that makes sense. The client is messed up (or I thought perhaps that's just what happens when they re-release a "complete pack" with stuff in it that yours didn't have). That's an extremely poor user experience, I'm kind of surprised they managed to do it on the same day they had a 75% off sale on that pack...