Hull card mystery

[truenorth01]

In the quest for the whereabouts of my Fathers old skiff SK-18-398 I ended up buying Sk-18-414. I recieved Hull cards on both boats. In the corner where it shows where the boat was delivered to there are hand written dates My boat 414 has a 1956 date of delivery. My Dads hull number 398 has a hand written date of 1954. My older Brother swears Dads boat was a 1956. Obviously my 414 was built after 398. Does anyone have thoughts on this. Also, what is a B O S number?

I made a post on my Dads boat but accidentally put it under Fiberglass Research area.

Thanks for looking.

Mark S