I have acquired several Selmer soloists after receiving one SS as "case candy" with a Vito Alto, and became a fan. Yours is a long shank, which AFAIK is less desirable,
although more desirable as an original "D" facing. It seems that C , C* etc. pieces were included with newly purchased MKVI Saxes, thus the availability of these pieces.
I think a "D" would indicate that it was purchased on it's own, not a factory included piece,
I don't have any LS Alto's, but I have long and short shank Tenors, and I like the long shank Tenor better than the SS.
I have a LS Bari, and am still interested in experiencing the elusive SS Bari, but would not pay big $$ for it.
There must be some reason that Selmer changed from SS to LS.