There is btw a whole series of small frame 75cc models unique to MotoVespa:
Vespa 75 08C
Vespa 75 U-2 PR 9.300.001
Vespa 75 Primavera T3 PN 9.320.001
Vespa 75 PK Primavera PK 9.330.001
Vespa PK 75 S Electronic 3 56 C 00011
Vespa PK 75 S Elestart 67 C 00011
Vespa 75 Junior (PK 75 S Electronic 3) PS 9.350.001 or 72C
Vespa 75 XL 96 C 00011
Vespa 75 FL Elestart 127 C 00011
The range starts in 1967 with the 08C which was equal to the 50 of the day. Apparently very few were produced until the PK versions the first of which (aka known as model Junior) had no indicators are were the only such of the PK.
And that is the extend of info I can find
If anyone has more I would lóve to know.
I kind of like the idea this is a MotoVespa only thing.