Those WOF's came in in the mid 1980's,they replaced the old white paper with black number WOF's.The old WOF's were too easy to photocopy,or people used to cut numbers off calendars and stick them over the numbers to extend their warrants.The new design was a step backwards as the numbers were hard too read from a distance and you had to put your head in the car to read the expiry date.I was in the MOT back then.A WOF cost .50c at the testing station back then.