Regarding the last two digits being the year - that's only true from about the 1990s onward when there became a standard for Hull Identification Numbers:
AA BBB CCCCC DE FF
AA = country code (GB = UK)
BBB = Builder identifier (AVB = Avon)
CCCCC = anything the builder wants to put
D = month on manufacture (A=Jan, B=Feb, C=March etc)
E = year of manufacture (6 could be 1996, 2006 or 2016)
F = Model year (96 = 1996, 06 = 2006, 16 = 2016 etc)
You sometimes have to deduce the year of manufacture form the model year.
It's not uncommon to have a number finishing B3 07. Which would be a Feb 2013 build, 2007 model.
Before the mid 1990s this standard didn't exist so serial numbers can't always be relied upon as manufacturers used all sorts of codes.
Sealine, for example, used the number plate letters - so a 1989 boat would have an F or a G somewhere at the end of the number.