Very old Americans at least still do this as well. My 100 year old grandma insists that using the wife's first name is only appropriate when the husband is dece

Very old Americans at least still do this as well. My 100 year old grandma insists that using the wife's first name is only appropriate when the husband is deceased. My wife has a 100 year old grandfather and he until recently followed the rule as well. His last letter he addressed to my wife specifically using her own first name. This was a strange way to learn of my own death.