I have been expanding my items and I recently started buying all the cheap items such as Gladiator, Chronos, and Orc I just got full Gladiator and I didn't get the achievement saying I have full Gladiator.
If you could tell me why that'll help me a lot.
Achievements update on a daily basis, so just ensure the items are in your inventory for 24 hours and you'll be fine. Also, I may just be making this up, but I recall something weird about sets, maybe unpack them to be sure.