This is licenses and contracts, not theory. It's lawyers and cowboying up.
If it were me, I'd say that the license files should be _authored_ by someone in the company who has a say on such matters. Come on, if it's work for hire, the copyrights by default don't belong to you, so you don't go licensing it left and right, it's your employer's prerogative!
To put it another way, the legality matters less than the relationship. A lawyer can communicate with the former employer in a way that mitigates potential problems. Or say it is unlikely to be a problem.