[Note: old thread, ack'd.]
I have no basis upon which to proceed with this assertion, but I believe most members reading this will allow that a TPGS is comprised of individuals bearing titles, grading finalizer, or jr/sr grading finalizer (or by whatever name locally used) whose activities can be reduced to a signature style.
What your coin grades, at any interval along a time continuum, has as much to do with the TPGS to which it has been submitted as well as the TPG assigned to pore over its details.
The entity, TPGS, and TPG, is overly broad for what essentially is a process involved in decision-making and rendering an opinion on behalf of a business.
I believe when a dissatisfied customer re-submits a coin he is seeking an appraisal ideally from another individual.
A reluctance to attribute proof coins as CAMs, and equivocation on those deemed high-level or borderline UCAMs may very well reflect, or be a consequence of either firm policy and/or an individual grader's stance on this particular issue. IMHO.