I do find the comment about the cab cars being "40 years" to be a bit out of left field, considering that they are all being upgraded to the same standard as the new ones and all the refurbished coaches ride just as well as the new coaches. Unless you are a buff, there is really no way to tell the difference between a refurbished old coach and a new one.
All of the newer coaches, which have been demoted to passenger cars, have been so at least since 2018, some of them earlier. The cars which are getting refurbished now underwent much the same treatment, but since they're in line to be refurbished now, it makes sense to reactivate them now rather than to bother with the unrefurbished Series VII cars which are not due for refurbishment at present.