I have done the search couldn't find anything on this subject,
what do you call an error of design in the subject or design of a stamp. for example St Kitts Nevis Columbus issue has him looking through a telescope which is an error as Columbus was around in the 15th Century but the telescopes where only invented in the 16th century, USA Boston tea party issue had the moon stuck in the rigging. I read somewhere its called a "Plot Error" but can find no other reference to it.
(sound a few people scurrying to check the Tea Party stamps)HeeHee
If anyone could shed light on this it would be greatly appreciated.