The whole P3/RP3 thing is mostly just when it was produced. But, a lot of people, myself included, tend to inadvertently use them interchangeably. Often people will call a P3 an RP3 thinking that it's a Rega P3, not a Rega RP3. shame on Rega for making it confusing like that! Best thing, if you can is to find out what the date code or year produced is, and the tonearm that's installed. Rega did introduce a new P3 late last year iirc, adding to the confusion.
Main: JMLab Mezzo Utopias, Oracle Delphi Mk 1/6, SME V, Koetsu Urushi Vermillion, AR Ref3, AR Ref Phono2 SE, AR Ref-75, AR CD3, Sec / LR: Rega P6/RB2K Lim Iso base, Acrylic skeletal plinth/braces, dbl pulley, gt sub, Sum Celebration, Anthem AVM60, Krell 402e, Totem Mani-2, 2X Anthem MCA50, PH-1