Though the coins I've found, and have also been given be fellow geocachers at events, say to keep. Unless pathtags are different then the coins you're referring to.
Other than that I had found a trackable marked as missing from several years ago. I'm still hoping to hear back from the owner as it was in a container but not placed in the app inventory. I found it interesting to find a missing one but feel bad that it went missing in the first place. I agree that with trackables, you have to go with the mindset that some people might end up keeping them.