How Is This Possible ?

I would guess that there where collectors then. I read somewhere that collecting coins first started with the kings and queens. Which makes sense since they would have been most likely to afford saving coins for their desire. It's also likely that some coins where put some place like a safe or hiding spot and forgotten about until discovered many years later.

The coins could have also survived by a hoarder, who hid them away.

Yes, the higher denominations have often been hoarded. Just like some people now hoard precious metal bars.
And also yes, many of the aristocracy and rich people prided themselves to have a "Münzkabinett" (coin collection) containing more valuable or rare pieces.
Some of those collection became the basis for museum collections.
Different to the USA where there are only a few museum which have a (substantial) coin collection, many European museums even smaller ones have a coin collection. And to make room or just to make needed money, museums sell off surplus stock.
Here the picture of the "Münzkabinett" of one of the museums in Berlin:



From http://www.smb.museum/en/museums-an...tt/home.html

May not be true. I started collecting long before that.


Good grief. Someone else had my idea.
Actually one of the reasons some coins pop up looking so new when they could be well into the hundreds of years is due to China. They, and a few other places, just make them again and again.

Thanks everyone Very informative . Any museums or collections that can be browse online ?

There's a somewhat infamous story of some very high grade 1790s large cent accidentally found in Switzerland by a dealer. The story goes that some guy from Switzerland went to the US way back then, then for some reason returned and brought the coin, which had then remained in the family for nearly two centuries (until bought by the dealer).

I won't be surprised if there are some coins around that were kept similarly for even longer (though probably not quite all the way since antiquity).

I do always wonder where does the known legend come from on all the 5th century Roman bronzes - they never seem to come up with any major amounts of legend remaining. Apparently it's a combination of three things: 1) examples with some readable legend do appear often enough to read the legend by combining known parts; 2) in some cases we can guess by similarity to known legends; and 3) for some later coins - of Zeno in particular - the legend is indeed not known fully.