Are good manners a barrier to genealogy?

Until the 1960s, it was unthinkable that any well-brought-up child would use the given name of an adult in conversation. You learned very early that the proper way to address your parent's friends was as Mr and Mrs Brown.

Of course, if the visitors were well known to the family and you saw them often, you might be invited to call them Uncle Fred and Aunt Gladys. And therein lies the problem.

Over the years I think I managed to sort out the distinction between my "real" uncles and those who had a courtesy title (for want of a better description); but what happens if I am reviewing some old letters that contain a reference to Uncle Bill.

Should I look for a link to an actual blood-relation of the distant cousin who penned the note (someone who might also be in our tree) or just his father's good friend from the tennis club?

I am a great believer in FAN genealogy (tracking friends, associates and neighbours of our ancestors) but when children spoke of them with the same title they used for their parents' siblings, it can be quite a challenge.