The passage you found is better than a "best guess," Sharon. I regard it as
a dead cert that it's the very passage Mark Twain's correspondent was
thinking of. His wording is a little different, but it contains all the key
elements of the TRAMP ABROAD passage. Moreover, I can appreciate why he
singled it out as a favorite: When read in its entirety, the anecdote about
uncertain identities is very funny. It was one of my father's favorite Mark
Twain passages; he would laugh till tears came to his eyes when he told
others about it. I'm getting old enough myself to appreciate it more every
year. These days I often meet people who seem already to know me but whom I
can't quite place.

Thanks very much, Sharon. You've saved me the embarrassment of sending my
book to press with a simple research question unanswered.

You don't happen to read Pitman shorthand, do you?

Kent