Anachronistic coins make no sense

Marty pays with coins. Coins from 1985, actually - those coins have the 'vibes' or 'feel' of the year 1985, but we can put that aside for the fact that coins usually have the year printed (or is that 'minted'?) on them.

Now, what are the chances that ALL of his coins he uses to pay (and carelessly leaves on the counter) have they year 1955 or some earlier year printed on them? Not very high, I imagine.

There HAVE to be coins that display a year later than 1955, anything up to 1985, right? There could be brand new '1985' coins on the counter, which would present a big problem that would DEFINITELY change history - if not for any other reason, then 'perfect counterfit coins' existing in 1955 - but who would bother to counterfit chump change? This would raise some eyebrows somewhere, that would have otherwise remained unrisen.

It doesn't matter if the cafe owner notices the years or whatnot, surely by 1985 SOMEONE would've paid attention to these perfect coins that just happen to have a future date printed on them, a coins do circulate. This could have changed history in so many ways, and definitely would in some big way that might affect not only Hill Valley, but the whole world!

It makes no sense that Marty would just leave them on the counter, or that he wouldn't even think of that. He's not an idiot, is he?

All that would've been needed to fix this nonsense is a short scene, where Marty meticulously and carefully checks the coins for dates, then sighs of relief, finding some with '1955' or earlier printed on them and uses only them to pay. Problem solved.

As it is now, it makes no sense.

At any rate, the 1985 that Marty returns to, should be VASTLY different due to this little anachronistic mistake alone.