36ZP18P, The first model in the picture frame series. Now obsolete.
36ZP18G, - No such model. The P & Q versions have a (B) or (G) suffix on the serial number to indicate the intended market - Britain or Germany (continental europe). It is probably a retailer using the older toshiba lableling which had the B & G in the main title.
36ZP18Q - Replaced the the P. It is the current model.
I like the Panasonic TVs but they do suffer from moire.. If you don't know what that is then don't look for it - It'll probably kill off your viewing pleasure. I've owned a ZP18Q before and if you must have it its a pretty sweet TV when working well.
This is usally how Powerhouse lable their Tosh TVs. I got my Tosh 32ZD26P from them and although the box staed as such - they called it a 32ZDKIT I think its something to do with price matching - "can't be the same TV cheaper Sir, It is a different modle number"