From my understanding, Yamaha made the Solid Bass 75 and 55 for two years, seems how well they were received and then launched the Super Bass line..the numbers indicate prices in Yen. The 75 had higher quality materials ie. Abalone inlays, Ebony fret board, quarter sawn neck and a Matoh ( related to Maghogany) body.
The 75 cost too much to make and buy so they kept the dimensions the same for the SB500s etc, but did away with fancy materials etc. They also sculpted the headstock a bit to move away from the shovel head look, which I actually find quite cool.
This bass has twice as much tone and sustain as a USA Fender.
I love it ! Plus it came with the original case