Miraphone Rotor Identification Needed

[Polkahero]

I'm trying to identify a rotor that didn't belong in a vintage 186 BBb that I recently purchased. Emailed Miraphone and haven't gotten a response, maybe someone on here knows. The 186 rotors are all stamped with the number 68, this one is stamped with the number 33. Has four bearing marks similar to the 186 so it probably came from a fourth valve casing. Five-sided stem similar to the 186 model as well. Any ideas?

[Polkahero]

If you have a caliper, What's the bore through the valve? And the width as well

I do have a digital caliper. The bore measures 0.80 inches and the width is 1.32 inches.

[Polkahero]

So Miraphone is telling me this is a rotor from a 1980s-era 186 model. Does anyone know when Miraphone switched from the pentagonal stem shape to their current "D" shaped stem? Trying to narrow this down a little further.