They may. I think it is BS. If you are burning it off, where is it going? The getter? It probably should have come off in the factory during the vacuum process or the other various heating processes used to reach the vacuum needed.
https://www.youtube.com/watch?v=8n4WVRKkmww If they don't, the burning off is largely useless in a vacuum unless what is burning off is an element absorbed by the getter. If it there are things like that, the tubes are heated and tested at the factory (at least for any new tube I would buy), so I am not sure what we are burning off once they reach us. I know, I am once again unconventional, but I think it BS. If you read some of the old tube testing done on old tubes, you would think even less of this whole burn in process. I think there is time needed to warm the tube up, but that is all. If there is some impurity in the coating on the tube that needs to be burned off, well, I don't want that tube. If it is thoriated tungsten and it is a used tube/needs regeneration, I understand "burn off" more, but that is a function of electron's being heated to the surface. That does not happen with coated oxide filaments or indirectly heated tubes...