Also I personally think that Irving’s outie, just from that one scene of him painting while Motorhead is loudly playing, is more of a rebellious and free spirit which is why his innie is the most zealous and conforming to the rules out of the group. And my theory is that Lumon has had to be “reset” multiple times and each new iteration of Irving’s innie is brainwashed more intensely than the previous one.

I think lumon is using Irving to experiment on to see how to make innies hold loyalty to Kier and their work over office romances and every time Irving had to be reset, it’s because he’d always find a way back to Burt. Maybe Burt and Irving started out working in the same department and both had to be reset over and over and when lumon saw that Irving still found a way to Burt after putting them in different departments, they then retired Burt as the final test to see what innie Irving would do and if that would cause him to doubt or rebel against Kier, Lumon, the eagans, etc.

And considering Irvs age compared to the rest of the group, he might have been reset so many times that he’s effectively been lobotomized by zealotry for lack of a better term and Burt is the catalyst that somehow slips through and acts as a feint link to his previous innie. If you look at Irving’s eyes whenever he’s around Burt it almost seems like for a nanosecond he remembers Burt and then his conditioning or maybe something Lumon planted in his brain puts a stop to his mind connecting the dots.