Yeah Doffs from that store are bound. You didn't make a mistake per se, though a lot of those officers aren't the best.
If you want to improve the quality of your officer set you should focus on the colonial assignment chains. Do you know what these are? At the end of each chain you get a unique rare doff and from then on you can repeatedly run Support assignments which will give you refugees which you can trade into a chance for blue or purple officers in Asylum assignments.
Join the chat channel "Doffjobs" ingame if you need help with the colonial chains.
Oh, ok. Yeah I'm working on one of those chains now. just finished #5 of 7 on one. I wondered where the refugees came from. Looks like I'm just going to have to buckle down and work more colonial assignments. I've been focusing on Diplomatic so far. Thanks for the info.