Something I noticed Burt said that points to him never being severed

When Irving finds Burt in his apartment, Burt is going through the notes Irving has written and reads from it “Goodman may have participated as a low level Lumon enforcer or goon” then says “that stings, we never used words like that” he pauses and clearly attempts to cover it and says “…with Lumon it’s very specific language”

All the more reason to believe Burt isn’t severed as he is referring to his interactions he had with Irving on the severed floor and is familiar with the way they would communicate, seemingly surprised that the word ‘goon’ would be a word in Irving’s lexicon.