Inheritance/BoM/Fortress also works.
I asked DXV a question about "when is something yours" somewhere in the previews, and he said pretty much the same thing.
I'm still not quite sure what happens when you buy Estate with token on Messenger... I think you do still get the gain though.
Not exactly sure how this one goes, but buying an Estate as Messenger, choosing Estate as the card you are gaining. But you reveal Trader, instead gaining Silver. Your opponent does not, and gains the last Estate in the Supply. Now, you resolve the original buy, but there are no Estates to gain...
You have one "it", the card you bought(Estate), and another "it", the card you gained via Messenger(also happens to be Estate). But you revealed Trader to the second "it", not the first "it".
So you bought an Estate, which should be yours, but it isn't(it's in your opponent's discard pile...)
Now, if these two "it"s referred to the same physical card, this problem would be solved. But they can't; otherwise, Talisman wouldn't work: you would buy a card, gaining the copy, which refers to the same physical card that you bought, and then you would try to gain that card which is in your discard pile. So they have to be different instances.