Best thing to do is call Hagerty & explain your situation. You do NEED to have a DD & prove ownership/insurance on it before they will consider. I had some issues trying to get my truck covered in the beginning as they are not really in the business of covering '80s/'90s cars/trucks. I pointed them to my web site & gave them a little back story about the truck before it was even considered. Before I had done that, it was a solid ‘no’ due to the year of it.
Now that Hagerty covers it, they treat it as an exotic & the price is alot higher than my GTO is (which has $15k more coverage), but still cheaper than what I was paying from State Farm and it is covered at an agreed value, which State Farm does not do. If it still were covered by state farm, I would get very little in a complete loss situation.
Blue book means nothing due to the agreed value.