Most copyright notices on these pages are invalid, so they would not serve as valid notice anyway, so your presumption is wrong (it also reminds me of the bear patrol episode from the simpsons)
First, the form is often wrong, which makes it the same as no notice.
Second, if the date is wrong, it depends.
If you use too early a date, you lose that many years of protection.
If you use a date 1 year or more after first publication, it's the same as no notice
So what you get by using wrong notices can be worse than nothing. You actually lose some protection.
As for the rest of the reason not to do it, because it's complete an total cargo cult lawyering that wastes tons of time?
You think you are getting something. You are getting worse than nothing. You are wasting time (this thread etc) figuring out how and when to update something, and whether it's legally correct, etc.
