In his 1960 Archaeology article "Monasteries and their Manuscripts", Morton Smith does use an interesting phrase that resembles Hunter’s words in the novel The Mystery of Mar Saba. We read that
Almost all the material is of the seventeenth century and later. The earlier manuscripts were carried to Jerusalem in the mid-nineteenth century, by order of the Patriarch, and now form the well known Mar Saba collection in the central library of the Patriarchate. (“Monasteries”, p. 177)
Here we see Smith again using “almost all”, but in a different context: he is describing the date of the material, not its fate. It’s still possible that the “-most” in “almost” finds its source in Hunter’s novel, but it would more likely seem that the phrase “almost all” is just a particular reflex of Smith’s personal syntax. To be fair, Watson himself does not draw a comparison with this phrase. And the remainder of this sentence does not indicate any similarity with Hunter’s novel, so there is no evidence of influence here.
However, earlier in the article, there is an interesting phrase which does resemble Hunter’s words. We read that