How the engine years
are worked out:
It is to the best of my knowledge but
could easily have mistakes. That’s why I want people to try it and see
if I am accurate with bikes that they actually own.

For most models, the frame prefix and engine prefix are unique. For
example the last GS150 model started with a frame number of VS5T*52364*
and a motor number of VS5M*52364* for the year of 1959. It is rare that
the frame and motor numbers are the same but I am assuming they reflect
the same year range (ex: frame numbers VS5T*52364* to VS5T*70128*
denote a 1959 bike so I assumed that engine numbers VS5M*52364* to
VS5M*70128* denote the same year range for motors).

Some models don’t fall into this assumption because two models shared
the same motor. The TS125 and the P125X share the same VNL3M*xxxxxx*
motor prefix and the Rally 200 and all further 200 models all share the
same VSE1M*xxxxxx* motor prefix so here’s what I assumed for this
search engine:

**VNL3M:** There were 28744 125TSs made starting with
VNL3M*001101* so I assumed the P125X numbers start at VNL3M*29846*

**VSE1M:** There were 41274 Rally 200s made starting with
VSE1M*001001* so I assumed the P200E engine numbers start at
VSE1M*42275*. There was a large jump in numbers between the P200 and
PX200 so I returned the motor numbers to matching the frame numbers
from the PX200 on.

I don’t know for sure if any other models share engines but I suspect
that the Vespa 90SS and the Vespa 90R share the same V9SS1M motor
serial prefix.