I think all versions with the extra "33 1/3" are rare because it was a mistake on the label that was quickly removed - it had been part of the label design on the old Gold and Black LPs, but the new yellow+black label design already had a much larger "33 1/3" logo above the Parlophone wording, so the extra small "33 1/3" was not needed.
And stereo versions of the early albums are rarer than the mono ones anyway.
The 1G and 1P stamper numbers mean it is an early pressing, but I think those early stereo PPM albums were pressed in small numbers so you would expect the stamper numbers to be low anyway.
Does it have the front cover with the Angus McBean credit over to the far right, or is there a gap after McBean and the edge of the sleeve? Probably wouldn't make much difference to the value - I'm just curious if they were still using the original batch of covers or had moved to the newer pressing with the credit moved over to the left a bit.
And what sort of condition is it in? The condition is obviously very important for vinyl collectors.
I don't have a stereo copy of PPM myself, so well done for even having one, never mind having a one that is rarer than your average copy!!