As I tell people who are interested in Vedanta ‘Time exists so that everything doesn’t happen at once.’
Even more so for fictional chronologies!
I think that there is some evidence that Enid Blyton did have an idea of a chronological sequence, but the success of the Five series meant that later books had to be squeezed into the time-frame.
Co-incidentally, my original reprint copy of
Five Go Down to the Sea arrived today, and Eileen Soper’s illustrations show Julian and Dick as almost fully grown young men. In one illustration poor George, who is still quite insistent on being addressed and treated as boy, showing signs of voluminous chest development - so I think in reality s/he would have been binding or de-emphasising that unfortunate development as much as possible, which seems to be the case in other illustrations in the book. (The dust-jacket artwork shows George with a distinctly masculine appearance compared with Anne, who is rendered as delicately feminine throughout.)
I think we can take the first twelve books as representing the time-frame scheme for the series. Not that Enid expressly intended to stop there, but it pretty much takes the children from 10-11-12 year olds to 14-15-16 at least.
Enid Blyton rigorously avoided any direct reference to current events or conditions, but nevertheless the settings, the manners, the general ‘feeling’ that I get from
Five on a Treasure Island and the following titles say pre-WWII to me. As a child of the 50’s it seems more like my mother’s generation than my own. Aunt Fanny is very much in the mode of my grandmother, who was a thoroughly modern woman born in 1897, and who gave much freer rein to her daughters compared with the societal roles and controls she had experienced.
“To grow up in intimate association with nature – animal and vegetable – is an irreplaceable form of wealth and culture.”
~Miles Franklin, Childhood At Brindabella: My First Ten Years