The color has been discontinued for a while and to my knowledge, trans orange was only offered for a short while. Music Man only builds what the stores order so if it was only offered for a few years, that means not many were ordered and thus a trans orange EBMM Bass is rare. Then you add the piezo option. Those too are also discontinued and not to many people ordered them. So yes, you have a very rare bass. EBMM doesn’t usually release build numbers but if I had to guess, I would say yours is probably a one off. I highly doubt there is any other trans orange piezo Sterling basses out there.
I had 2 Bongo’s that were one off basses both with piezo bridges. I really wish that I still had them again, knowing now what I didn’t know when I sold them. The irony is my one Bongo just popped up on Reverb. I am so tempted to buy it back but there are other EBMM basses that I am wanting to get this year. If it was my other Bongo, I would do it but with the one for sale on Reverb, it is candy apple red (also a discontinued color now) but I sold it to finance my current candy apple red Bongo with an all rosewood neck.