Curious question: it doesn't look like I can repeat main missions to pick up specialists that I missed the first time around. For instance, I didn't get the Materials Engineer from Mission 14 the first time I tried it, and thus I can't even try to develop the Battle Dress 4 or 5 upgrades. If I go back and attempt to repeat the mission, I can identify the Materials Engineer as one of the prisoners, extract him via Fulton, and then complete the mission, but even if I do all that, I don't seem to get him/her back in my base. The specialty remains white in the mission selection screen, and I still can't develop the tech that they're supposed to unlock. Same goes for stuff like Cybernetics Specialist in 9, Anesthesia Specialist in 10, and a few others that I missed.
Is this a known bug or am I doing something wrong here? I've only tried Fultoning these people; I haven't tried dragging them back to a helicopter. Would that make a difference? Playing on PC/Steam if that's relevant.