HIN Ending In "C"?

[TrueMileageUnknown]

I've searched and only found a question at the end of a 2006 post with no answers. The HIN on my boat reads SECF0372M74C. I understand that the last couple digits typically denote the year it was built, so how did the C find it's way in there?

Thanks in advance!

[SeaPlusPlus]

C = October

The month it was manufactured in 1974.

Source:
http://boatsafe.com/nauticalknowhow/hin.htm

[TrueMileageUnknown]

Much appreciated, SeaPlusPlus! Thank you!