I don't know the S/N sequence for the Syssa engines. Early on they all seemed to be in order from #1. I didn't see any relation to year of production though that could have changed after mine was made.
The Syssa engine had tremendous potential but it became the product of a self centered, though extremely talented person who seemed offended when anyone suggested improvements or changes of any kind. There isn't a product made that can't be improved but he didn't see it that way. Sad! I'm not sure the design was very well tested before it went into production. Had the product been allowed to mature, I think it would still be produced today.