the old JCB dealer here (Power Equipment) no longer represents JCB.
I called them, they still had parts etc.... gave serial number. They not only knew the make/model and year, they ALSO knew who the original buyer was AND what was paid.
Now, to be fair, it's possible the machine was originally bought FROM them, I don't know. TVA (Tennessee Valley Authority) was the buyer but, my brother in law bought it in Crossville or Cookville, about 2 hours away so I was surprised that it came from TVA "locally".
None the less... simple answer, as has been said, call dealer give them the info on your plaque and wait for answers.
It looks identical to mine (1550-B) except mine isn't a site master, doesn't have the extend a hoe, doesn't have the clamshell bucket.... doesn't have 4wd.... but if you look past that, they're substantially similar and mine was around 1985-1987 when new (forget) but I'd feel that's a reasonable era for yours.