With any coin, unless there is a whole heap of them made then they are likely mint sport or a prototype (or similar).
I believe that the dies are made so they normally cannot be put into a production machine with 2 heads or 2 tails.
The only sceneries where I can see 2 heads or 2 tails is
1 That a die was incorrectly made to go in the wrong side of the machine, but that seems pretty unlikely and would lead to a large number of them which would be found in circulation. This has not really happened.
2. "Mint sport"
I don't consider double "head"/"tails" coins to be genuine errors made during production.
Sure they are rare and interesting, but I don't think they are errors.
When searching coins, I look at both sides, but not because I am looking for both sides to be the same.
The last one I heard of being found in circulation was a 2007 5c, but it's been a long time since that was reported, so I don't think there was many of them made.