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 2/3, SME309, Sumiko Celebration, AR CD3, Sutherland Insight, Moon P5, AR VT-100 Sec: Rega P6/RB900 Lim Iso base, Acrylic skeletal plinth/braces, dbl pulley, gt sub, DV 17D3, Anthem AVM60, 2X Bryston 4BSST, 2X Anthem MCA50, Acoustech PH-1, Totem M1 Sig