Every year at the start of January, a load of slightly too clever for their own good web devs post code snippets all over the Internet showing how you can automate updating your site footer. They are all doing it wrong, for the reasons others have already mentioned, and every year better informed web devs reply to try to correct them. The date(s) shown should be the date(s) from which your copyright runs, and nothing else. A brief conversation with any IP lawyer will confirm this for you. Unlike most matters of law, this one is remarkably consistent from place to place, because the basis is an international agreement that basically every country in the world you're ever going to care about is party to.
There is a small but non-zero risk that by using a later year than the correct one you will actually weaken any legal claim you might need to make. The other party might turn up in court and say, "Look, nathan_f77 only claimed copyright from 2020 on this work, and it's on my site with a date five years earlier!". So automatically updating the date without leaving the original dates in place is a particularly bad idea.
In reality, the main practical purpose served by such notices these days is deterrence: it makes clear that someone specific does claim the copyright, for the benefit of the kind of person who doesn't really know how copyright works and might otherwise assume that because something is on the Internet then it's OK for them to take and redistribute it. They'd lose a legal action anyway, but those are expensive and time-consuming and there may be little to gain from one if the damage caused is minimal, so avoiding it by staking a very obvious claim might be helpful in some situations.
There is a small but non-zero risk that by using a later year than the correct one you will actually weaken any legal claim you might need to make. The other party might turn up in court and say, "Look, nathan_f77 only claimed copyright from 2020 on this work, and it's on my site with a date five years earlier!". So automatically updating the date without leaving the original dates in place is a particularly bad idea.
In reality, the main practical purpose served by such notices these days is deterrence: it makes clear that someone specific does claim the copyright, for the benefit of the kind of person who doesn't really know how copyright works and might otherwise assume that because something is on the Internet then it's OK for them to take and redistribute it. They'd lose a legal action anyway, but those are expensive and time-consuming and there may be little to gain from one if the damage caused is minimal, so avoiding it by staking a very obvious claim might be helpful in some situations.