First off I save all the Barr notes I get. Not because I think a Barr is valuable, but because it is an old note from the 60's, so nice find there.
On the other I really don't think you can call that more than just a curiosity. Notes like that are not sought after by collectors. Here is one I found with a wet ink transfer. Even though you can clearly see most of the rear on the front it's really just a bad print job rather than an error note.

On the other I really don't think you can call that more than just a curiosity. Notes like that are not sought after by collectors. Here is one I found with a wet ink transfer. Even though you can clearly see most of the rear on the front it's really just a bad print job rather than an error note.























