Bad memory and lack of pictures/notes. I started thinking about the plastic lever orientation after tap replacements years ago, while trying to reuse the USA wonky lever. Scootermercato and Scooters Originali make note of the different taps used on USA models and different positions of the black lever with available replacement taps.
http://www.scootermercato.com/Scooter-Parts/Fuel-Taps-and-Parts/180056
http://scootersoriginali.com/products/vespa-conversion-plate-usa-fuel-rod-to-euro-rod
I have replaced at least six taps with the newer, non-USA types and used the black lever. I think it required disassembling the tap, rotating the disc 180 degrees, then also rotating the lever assembly so that the words were on the engine side of the selector. Up ON, center OFF, down RESERVE as original. Fuzzy on the details, but they do work.
I still have three of the P's with new taps and the words on the engine side that work as original.
I've looked at numerous online pictures and THINK the words were originally on the clutch side. I have one fuzzy picture of a rusty one owner P that followed me home that seems to show the lever and words on the clutch side. railfancwb may have an original. I don't really know.
hp explained it well in this thread:
P200 gas valve question