GB 1972 Christmas Sg 914 All Colours Missing

Hi all,

This is a stamp i've wanted for a while, all colours missing with just embossing showing, pierron states 100 copies known, there is no listing for it in my SG catalogue although my catalogue needs updating.

My question is would this be considered an error or just printers waste, a lot of pre decimal stamps have info on where the particular sheet was discovered or how it came to be but I cannot find info on this particular stamp.

thanks.