No, it's pretty straightforward Papalapin. Serial numbers for mid-60's and newer Howatts begin with the last digit of the year of manufacture. Example: a 1977 bow would be numbered 7XXX. As I said, the Triumph was made from the early 1970s to 1985, so serial number 6173 is a 1976 model. Where it gets more difficult is when you're dealing with a model (such as the Howatt Hunter) that was made for multiple decades. In that case, you have to know your model years....and I do.
I have no connection with the Howatt Plant in Yakima, or the Martin Headquarters in Walla Walla. I'm just an enthusiastic collector and Howatt historian.
Mike