Hi, we'll I just bought a Hobie 14, serial number 2123. Does that make it earlier than 1970? She still goes fine ! Bit leaky ... So, how do the 4 digit numbers work?
The short answer is yes - it's older than 1970. But how much older is tricky, especially in the early years.
The four-digit serial numbers were just that - serial numbers. Serial numbers up to around 6000 were used until the modern numbering scheme, mandated by federal law, was implemented in 1973.
In the early years, there was some correlation between sail number and hull number (but it's not exact). From old photos, you can guesstimate which numbers go with which years.
But basically, the lower the number, the older the boat.
I don't think Hobie Cat started with 0001, either. The lowest number I've seen/heard of is over 1000.