More generally: Can it be assumed, that the first letter always is the booking class with SQ?

I found on the web an internal paper from a travel agency, which translated many SQ-fare basis into booking class. Most had the same first letter in the fare basis as the booking class – except some starting with EY and YE which seems to be translated into almost anything.

H was not on that list. I actually have a fare basis HLTOPWB (CPH-SIN-SYD). Can I thrust this is a H-class ticket?