We kid around about calling in sick and how ridiculous it is for someone to have recurrent on one jet and then start initial on a different jet two weeks later but I think he could actually make a legitimate "safety" argument here.
I know there are lots of pilots qualified on multiple airplanes and they do it with no problems but there's got to be some degradation of knowledge retention involved. Limitations, procedures, etc.
Seems like a common sense rule should apply. It would benefit the company as well. Regarding costs and quality of training.
Maybe a 30 day rule.
Just a thought.