Oh, I'd lost this thread off my 'threads I'm on list'.
To get it going again, what words/things/concepts did you only notice on an adult reread of the books, whether because you just didn't notice it as a child, or because it was left out when the Armada paperbacks were omitted?
I've only just noticed a reference to 'fairy cycles' in Goes To It -- the incident when the Ozannes and Bride Bettany decide to do trick cycling through hoops and all crash and get black eyes. I looked them up and apparently they were a popular brand of children's bicycles and tricycles in the 20s.
Also just observing in Go To It the beginning of Joey as Special Spirit of the School Person, when the prefects are discussing the problem of Betty Wynne-Davies and Elizabeth Arnett and say they wish Joey wasn't so booked up now, but decide to invite her to their next prefects' meeting anyway.
Obviously, that reads quite naturally when you look back from the later books when Joey regularly intervenes, but at this point in time it seems quite arbitrary that they want to consult her -- they have loads of recent CS Old Girls that they remember as prefects and Head Girls actually on the staff (including Mary Burnett, who has just arrived), who are physically present, whose job it is to control naughty Middles and who are not three miles away dealing with three small babies and a husband absent at the Front...?