I've been a lurker for a few months now; finally signed up and have a mystery that I'd like help solving, please. And yes, it's about a marching baritone, but there doesn't seem to be a marchingbaritonetalk.com.

I bought a used marching baritone on Facebook, stamped with Boosey & Hawkes Regent. It has a 5-digit serial number on the 2nd valve, 03283. The serial number/date information I've found shows Boosey/Besson/B&H production with only 5 digits in the serial number as over 100 years old, which is not the case with this horn. It seems like when B&H stopped making instruments, they wiped out any information about their manufacturing.
When I bought a Besson London 600 series tenor trombone on Facebook, eventually I found information matching the serial number to a model 639 made in the mid-90s. But no such luck with this marching baritone.
Does anyone have guidance for me, please?
Thanks--
Steve