Of course a physical exam can be enough for a GP to refer, so possibly that's why, he was confident enough from that to send to to rheumatology? Seems he got far more out the the fortnight he probably had covering Rheumatology in his GP training than the Rheumy who did years of training to specialise, the GP you saw who seemed to recognise that typical symptoms aren't always there. Begs the question why the initial Rheumy didn't seem to know that maybe you showed signs of PsA as the other two did.
Re your question, as I mentioned in one of my replies to suzannedale, any Rheumy would take his own tests, if that means retesting then fine but he should never rely on a GP's or even another Rheumy's results for baseline tests when he takes on a new patient. Obviously it's a no control situation, it's entirely the choice of each one. I don't believe there's overuse by GP's because they're advised they can't refer willy nilly so they need to be sure it's necessary , that means an examination, ESR/CRP, RF & anti-CCP if it's determined necessary, though we know taking the latter doesn't always follow. It's feasible that Rheumy's don't bother with RF as anti-CCP is a more reliable test, plus examinations & full blood count may be enough in most newly referred patients. This would explain he discrepancy in RF between PC & Specialists maybe, not necessarily overuse but seen as less necessary in secondary care?