Roger that, numismatic gold is usually encased in a thick plastic container to prevent just such an event from happening.
My bullion coins were minted a hundred years ago and were actually carried around in someones pocket so the wear and scratch marks are readily apparent. Go ahead, bite one, hell cut it in half if you want to, nothing in there but pure gold.
I prefer the common date 100 year old coins as well, they have historical and a bit of numismatic value, and can always be melted as the need arises.
If they were minted 100 years ago, they are probably 90% gold.