[65Bowrider]

I don't know all the rules on registering a boat, but the info that I have is:
Our 21' is a 1962, hull Id #71 ... Manuf name is spelled out "Sea Craft" with Florida registration # FL 7162F. It has remained in Florida since 'birth'.

The UNOHU, a 21' is a 1965, hull #167. My guess then is IslandTrader's 21, #136 was built between a 63 and 65.

Our Bowriders are 1965 & 1966, hull #336 & 319 respectively, supporting registration is the year, not built. Also indicating numbers were assigned by length since kerneltugboat is a 1969, #221.

Hope this helps.
Cheers.