To sum up, the following questions are up for grabs:(1) The definition of "P2P", a term mentioned by the OP in passing. Which would possibly reveal that mcmanus is measuring pivot to stylus tip, not P2S.
(2) The actual effective length of the tonearm.(3) The (remote) possibility that the wiring is dragging on the arm wand, or I'll add another, that the pivot bearings are too tight, preventing free movement of the arm wand (although that would probably not result in the cartridge skating all the way across the LP surface).(4) Diamond tip has fallen off the cantilever; it happens.
(2) The actual effective length of the tonearm.(3) The (remote) possibility that the wiring is dragging on the arm wand, or I'll add another, that the pivot bearings are too tight, preventing free movement of the arm wand (although that would probably not result in the cartridge skating all the way across the LP surface).(4) Diamond tip has fallen off the cantilever; it happens.