Disney movies and missing copyright dates

[BwanaBob]

(Maybe I've not seen enough of a sampling, so someone may correct me)

We have a boatload of Disney DVDs, (99% of them are animated flicks).

Wanting to sort them by release year I started looking for copyright year.
(Music CDs always seem to have this somewhere on the disc or jewel case.)

But these DVDs do not have copyright years printed on the discs or the backs of the cases.

Why would they do this?

[Exapno Mapcase]

I don't know why, but I've noticed that a lot of CDs, especially of releases of older albums, don't give a copyright date either.

However, just to note that since 1989 no copyright notice has been needed. Maybe they don't want even the extra few characters to deal with, or they don't want to remind people how old a product is before they buy it.

[garygnu]

...or they don't want to remind people how old a product is before they buy it.
Maybe, but Disney is currently lobbying for extended copyright periods. Are they related? I dunno.
I also noticed there is a copyright date on Pixar movies, but not on other Disney movies (Sixth Sense, etc.).