Martin, These Miss-perforated stamps never become Errors, if the stamps are drastically misaligned they are usually called "freaks". The more misaligned, the more collectable. In your case the stamp is just badly centered. An Imperforate stamp that should have been perforated would be an Error, or a Row of Missing Perforations creating a Imperforate Between Pair would be an Error. Hope this helps. https://www.hipstamp.com/store/harry-patsalos-philatelics
Generally for perf or color mis-registrations to be considered an error, the shifts have to be around 50% off. You would also want the stamp to be collected at least as a pair to show that it wasn't a fake perforation made through the middle of a stamp.
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These Miss-perforated stamps never become Errors, if the stamps are drastically misaligned they are usually called "freaks". The more misaligned, the more collectable. In your case the stamp is just badly centered. An Imperforate stamp that should have been perforated would be an Error, or a Row of Missing Perforations creating a Imperforate Between Pair would be an Error. Hope this helps.
https://www.hipstamp.com/store/harry-patsalos-philatelics