I can tell you for certain that I use Roman numerals on the copyright dates of the videos I make, because I grew up with Roman numeral copyright dates on the TV programmes I grew up watching - even children's programming had it.
For some reason the one that sticks in my mind is the Blue Peter one with a copyright symbol, the old "three boxes" BBC logo, date in Roman numerals and the little stylised sailing ship logo :-)
Anyway, long story short, I use Roman numerals for copyright dates because fancy like.
Interestingly, that's less of a thing over here. e.g., productions of the public broadcasters in Germany usually end with the date in Arabic numerals. Including Sesame Street.
The BBC didn't have copyright statements at the end of the credits until the early 1970s, and initially they used Arabic numerals, but after a couple of years later (the mid/late 70s) switched to Roman numerals, which they've stuck with since. I think the changeover is around the time end credits and channel logos stopped indicating "Colour".
IIRC in 1999 one of the trailers for the BBC's millennium coverage involved years counting up to MM in Roman numerals, which seemed perhaps to be a nod to their use of them in credits.
For some reason the one that sticks in my mind is the Blue Peter one with a copyright symbol, the old "three boxes" BBC logo, date in Roman numerals and the little stylised sailing ship logo :-)
Anyway, long story short, I use Roman numerals for copyright dates because fancy like.