Remember to adjust for inflation...
To get the true price in today's $$. '81 was right before the start of the galloping inflation of the Carter years, so a selling price of $50k (just an example, not the price of the '81 Hunter) in '81 would be $120k in today's $$. That also drives the prices of used boats up...so it's not surprising to see 25 yr old boats for sale today at a price that's higher than the original...or seems to be till you adjust for inflation.
Then there's stuff like the economy, both local and national. As an example, we were in a recession in 1992 when my husband died... the boat market was so depressed that the "fair market price" then for the boat we'd bought for $70k in '89 was only about $45k. The economy was on a roll again--the "dot com bubble" was in full swing--by the time I sold it in '96, pushing boat prices back up. I got $65k for her.
Trying to sort out what anything, especially "luxuries" like boats, snowmobiles, RVs etc, should be worth at any given time can turn your brain to mush...there are too many variables one year to the next. So I wouldn't worry about what the original price new was...the only thing that matters is, what's a fair price for it today, in today's economic conditions.