I think the fuss is FFF that alot of differences training done on VP, retractable, turbo's and pressurisation done by FI's since lasors started stating its point of view will actually be defunct.
Alot of instructors myself included have done and signed off differences training on students while being not legally being qualified to be PIC on the various differences on SEP's if our MEP experence is not counted. I suspect that the majority of Pressurisation signoff's are done by Instructors who have type ratings on Pref A machines.
I will be willing to bet if you asked to see your Instructors log book they won't have the required entries in thier log books yet they will sign yours.