... because otherwise the next thing we know will be it appearing on
ebay with a £1M price tag! We will all suck our teeth at the lunacy of youth, it will not sell and he or she will go away disillusioned. Worse still, one of the rag newspapers will pick it up and report "Rare 20p selling for £1M" and we will be deluged with other similar listings.
The fact is
The Royal Mint is producing coins to a much lower quality than in the past and these minting flaws are getting more and more common. Someone on another forum did a study of the new 2016 £1 coins - of 64 coins examined he picked up 36 different minting flaws and virtually every coin had some flaw somewhere. If we are going to call every one of those an error coin and start collecting them we will all end up in the madhouse.