It's not the easiest thing to understand, as you get conflicting info from the RYA, BMIF and RINA.
I still build to the original set of regs that I conformed to when I achieved my RCD certification.
Having had a re-read of the HIN ruling, (first time in the last 10 years
) it seems the last 2 digits are indeed the model year, which to me is a bit confusing, as I'm used to US boats having the last 2 as the year of manufacture.