We can measure impurities and isotopes extremely well, which is what the post I responded to mentioned. This is very mature technology.

You're right that we don't know what new branches of science might be developed that could produce new insights from old artifacts.

But remember the situation. My idea makes it possible to record and analyze ancient finds that currently just disappear. It only gets us 99% of what we want, but in the current system we get 0%.

https://www.logicallyfallacious.com/logicalfallacies/Nirvana...

The isotopes were just an arbitrary example. The important bit was at the end "or something else we don't know yet". Granted I'd guess that's fairly unlikely for coins specifically.

> currently just disappear

They don't though. The preferences are as other comments have described - to stash the artifacts away in storage or to leave them in the ground for excavation in the future.

Whether or not the laws and common practices are fair to the people who discover the items is a separate matter.