The bottom bracket underside shot gives a strong and anti case for the bike. Note the small stampings above the downtube socket window, Alberto used to stamp a date code there, month and the last two digits of the year. The against is the absence of an M cut out of any type.
Maybe Alberto was considering making a pricepoint bike in Italy for the Europeans, many other significant names in Italian road bikes at the time were. While Alberto had a steady market for the Volumetrica, the Prestige did not go away.
In the 60's almost all Masis were Masi Specials. With a few exceptions I have seen. Both road and pista bikes were Specials.
The Gran Criterium arrived in 1970 to the public and while there were a few Specials to be made after, in short order the Special was pnly for the pista bikes.
It stayed that way till the Prestige that arrived in 1975 as close as I can tell. The Gran Criterium apparently continued till about 1978. Maybe the GC was dad's model? Also a Faliero Masi shows up in the middle 70's on a few bikes.
If Alberto acknowledges the bike, it probably had the headtube graphic seen in about the middle of this selection with the lower case m and white background.