This seems trivial? Just like any other asset when you are alive, if you cannot establish a cost basis it’s assumed at $0.

Easy stuff. If your benefactors care about taxes on their estate they will properly document capital assets. If not? Oh well. It was a windfall gain either way.

This is such a non-issue given the inheritance/gift tax limit being so high I don’t understand why it’s ever talked about.

It’s also not as onerous as people assume. I’ve established cost basis 15 years later on an asset I had no paperwork for by simply looking up the daily average price for said asset when I knew I acquired it. This can even be used for stuff like buying an expensive retail purchase - just use advertised retail cost. The IRS allows broad leeway so long as you are consistent and can explain your reasoning.