There is nothing wrong in taking the Stanley Gibbon meaning for the term used.
So long as you do not think that the rest of the world or someone from inside or outside the UK selling to someone in the UK should share your same meaning to the term used.
The term used means to me!
Used can mean from 1st Day Cover, Maxicard, by mailing, cancelled to order, special cancels and no gum or cancel etc.
But I am not telling you to take on my meaning for used and I do not need to take on your meaning for the term used.
Everyone has a different meaning for the term used so in my description area I tell people what used means for my
ebay listings.
This is a very good issue to bring up. The term used in a global sense really challenged me to think long and hard about it all!
We really need to look at a stamp to see if it fits into our meaning of being used.