If I purchased a BC for $1 and the current market price is $1.50, my basis is $1 and my unrealized gain is $.50, but does that gain impact something being fungible? The coin is still mutually interchangeable at that point.

I keep reading examples of trading a baseball card. If I had two Babe Ruth cards, one in perfect condition and one with bent edges, the items aren't valued the same and most likely won't be directly traded for one another. They aren't fungible.