Although I don't collect error notes, this is what I would do.
First, I'd ask myself how this type of error could be created during the normal printing process. If I could come up with a plausible explanation on how, then they are potentially real error notes.
Then I'd search someplace like Heritage Auctions currency sold section and see if an error note of this type has ever been authenticated/sold. If so, then again they could potentially be real error notes.
In my case, I wouldn't be able to get past my first step, because I don't know how this type of error could be created by the normal BEP printing process. So, to me they say FAKE and I'd walk away.