Ab excerpt from a Boat US article.
For years, U.S. Coast Guard regulations required boat manufacturers to use August 1 of the previous year as the cutoff date for the next model year. For example, a boat built in September 2011 could be called a 2012 model, but if it was built in July, it had to be sold as a 2011.
In 2012, boat builders petitioned the Coast Guard to change the date to June 1, allowing for an extra two months of production to still be labeled as next year's model. Manufacturers argued that because of marine production schedules, which, unlike automaker schedules, tend to fall at erratic times throughout the year, they needed to have more flexibility in designating the time span of their new model year.
The Coast Guard agreed to make the change, permitting a couple of months of last year's boats to be called this year's.
The information with the boat's model year is contained in the hull identification number (HIN), which is a label permanently affixed to the boat. The number includes a date assigned by the builder. This date is technically not the date of manufacture; rather, it's the date on which the boat was certified by the builder to meet Coast Guard regulations.
Some boats, especially large ones, may be on the floor for months before completion (even straddling the June cutoff date), while others may be finished in a matter of days. To be consistent, the Coast Guard uses the date the manufacturer says the boat meets federal regs. Once the HIN is assigned and affixed, that date becomes the boat's model year, regardless of when it was actually finished.
