175 T-stat Markings?

[JoLin]

I found out a couple of days ago that, though my motor's model and serial number place it as a 1997, the powerhead is from a different year - I think 1995. I base this on the fact that the seller originally told me that the motor was a '95. I found this all out when I ordered thermostats for a '97 that are a completely different design from the old ones I removed from my motor. When I reordered them I had to guess at what 1995 model the powerhead might have come from. No way of knowing for sure.

Anyway, the new t-stats fit properly in the head, but the body of the stat is stamped 'B1C'. The old stats are stamped 'D1C'.

Anyone know what those markings mean?