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, MD FT101, Acoustech Ph1, Moon P5, AR VT-100. Sec: Rega P6/RB900 Lim Iso base, Acrylic skeletal plinth with braces, dbl pulley and weight, gt sub, DV 17D3, Anthem MRX700, 2 X Bryston 4BSST, Totem M1 Sig