Need help, but it's no biggie. How should one address a former Office holder?

[MADem]

21. And there's "social protocol," and I've seen examples of this usage back in the 1960s.

If you go into the newspaper archives (Google has some that are robust if cumbersome) you can see examples of "President Truman" and "President Eisenhower" into the sixties. There are some papers that are careful to do the "former" or "ex" and say "Mister" or "General" but there are others that didn't bother--even way back when.

People are unwilling to let go of a leader that they happened to like, and adherence to that writing style might very well depend upon the editorial lean of the paper as much as anything else.

And here's a little CBS thing about former President Johnson's library, filmed a year before he died, and in it a bunch of folks, including then-President Nixon, call LBJ "President Johnson."

Social usage--it's probably always going to butt up against official protocol. I don't think it'll ever change.