1985 - 1983?
I’m guessing 1985-1993, which roughly matches up with “cold storage for 25 years until present”. So basically it was approx five years of unknown storage, eight years of cold storage, another couple years of unknown storage, and then another 25 of cold storage. So maybe six or seven years of fade, depending on how it was treated during those other years… which from the looks of it, was pretty good treatment as well.
EDIT: Damn thread page breaks. DeLorean?!? Do tell! Did you need roads where you were going?