Judy, I don’t recall the usage of it either. I found this.
“Time Traveler for selfsame
The first known use of selfsame was in the 15th century”
It appears to me to be “An archaic word or sense is one that still has some current use but whose use has dwindled to a few specialized contexts, outside which it connotes old-fashioned language. In contrast, an obsolete word or sense is one that is no longer used at all. ... An outdated form of language is called archaic.”
You said the books are printed by the Mennonites. If they also write the books I can imagine they would probably use some archaic language.
You have become our researcher extraordinaire, Spunky!
Just catching up a bit....thanks for the info on “selfsame”. They definitely use some archaic language. The readers don’t use the word “morning”, they always say “forenoon”. I don’t mind at all, as it’s good to learn interesting expressions.