Can I still use old sea time not submitted before my first license?

Hello all, one of my licenses is a DDE Unlimited which I want to add a Chief of uninspected fishing vessel to. Apparently I need about 200 more days sea time to get my raise in grade. My question is… can I submit a sea time letter from a boat company I worked for before the dates of sea time I submitted for my first license? Does that make sense? I can probably track down sea time from 15 or 20 years ago that would probably add over 1000 days to my sea time. (If they are still in business)
Which brings me to another question I guess. What if a company is no longer around? Can you get a sea time letter from a previous captain? What if I was the captain? That’s probably enough to chew on for now. Any help would be greatly appreciated.