900ss Engine Number, Year?

The engine in my 1991 900ss isn’t the one it was born with, I read in another thread that ZDM means Ducati, 904 is the cc, 2 means 2 valve heads, C means carburettor, A means air cooled and that the engine numbers are sequential, does anyone know what year mine would’ve been produced (roughly?), it doesn’t really matter of course but it would be nice if it was a 1991.
Oh yes and what the star means?, just to make it look pretty?

 

Thanks Exige, Z = country, I’m a bit dim so can’t think why they would use Z ?

 

Darn it of course!, how come it doesn’t get mistaken with Zingland though!

 

Learn something every day, thanks Exige.(re the world region code).