I do not believe the lead number is a '7'. Current data suggests the serial numbers are purely sequential with no year designator and a '7' would be greatly out of sequence. The lead character actually appears to be several partial stampings of a '3', (see attached, highlighted photo). A '3' would be in sequence with the other submitted serial numbers. If you look at other photos, you'll see that Motobecane did use the flat topped version of the number.