mornington, yes, a collective research effort would be most excellent! I think I could probably get over the self-indulgence (my irrational aversion on this basis may well be mostly related to my recently-completed MSc dissertation which was definitely more labour than love by the end) but I would need to do some kind of lower-than-PhD level background training, I think, which is offputting at the minute. I have looked and looked for the links between my own discipline (a quantitative social science) and what I want to write about the Chalet school, and there are really, really none at all.
You will be sorry when you're at death's door with double triple quadruple pleuro-pneumonia and Robin is obediently not singing you back to life, my lamb. :(
More lengthy waffle, on late Armishire books: I am fond of Rosalie - it's not in my top five, and possibly not even in my top ten, but it's a sweet little book, if a bit of an unusual one. I think Rosalie is very sympathetically portrayed, compared to - what's the name of the wet girl in Malory Towers? You could imagine Rosalie being derided as wimpy and pathetic and shallow, but she really isn't - by author or classmates. I think she's very convincing as a new girl who struggles to adjust but gets there in the end, without even a proper near-death experience. The fancy dress evening is quite good - not the best evening entertainment ever, but definitely preferable to any pantomime, nativity or sale. And I'm oddly charmed by the scene in which Tom and Rosalie are sent to Miss Annersley in the library and Nell is sat in the background scowling at them and occasionally interrupting with "Miss Annersley asked you a question", "where's your curtsey?" etc. And there is a pleasing lack of Joey, who I do find quite hard going in the Armishire books.
Three Go (which I know isn't one of these odd three) is not a favourite of mine, though I know it's a popular one. I think this is the first time I've read it unabridged. The Gillian Linton/Peter Young romance is the best I can think of in the series, but that's not saying much. 
It is slightly marred by the use of the "she's too sweet and pretty to teach forever" line, last seen in reference to Simone, but I can see where it's coming from. Mary-Lou is believable and likeable as a younger girl, and Clem is brilliant - as is Verity - I forget how determined and self-possessed Verity is here, after she just becomes boringly dreamy in later books. Again, Joey is appropriately restrained which is a bonus. And it's nice to see the next generation of Tirolean girls popping up, too.
The gap between Gay (and everything leading up to it) and these last four is massive, though.