The first print to suggest 'show and tell' not 'show, don't tell' (that I know of) was published in 2006 by the Open University (Creative Writing Edited by Linda Anderson). There are books out there that do teach 'show and tell' and they've been teaching it for a while.
The earliest instance of either rule I've been able to find is a quote by Mary Flannery O'Connor (so no later than 1964), which says "Fiction is very seldom a matter of saying things, it is a matter of showing things" (quoted in Rozelle, Ron (2005) Description & Setting: Techniques and Exercises for Crafting a Believable World of People, Places, and Events, Writers Digest Books). I note that even then it was "very seldom", not "never". I suspect her quote got dumbed down by those who like absolute rules and can't cope with uncertainty. Creative Writing by Linda Anderson and Derek Neale was published by Routledge in 2005 -- I don't know what the relationship is to the book you cite (different publisher, and Anderson listed as an author, not an editor) but it gave the same advice a year earlier than your reference.
She Edited this version, D, (i.e.: Creative Writing, A Workbook with Readings, Edited by Linda Anderson. Published by Routledge; written and produced by the Open University (First published 2006). It's used as part as an A215 university course in CW. The author quoted on show and tell in her 2006 version is Derek Neale. It looks like she's been comissioned to bring together a collection of authors to teach this course and she uses Neale to explain show and tell. I agree it goes back further, but (for me anyway) that course reader is just the first definite teaching where it's mentioned 'most new writer's are met with 'show, don't tell.' and then goes onto highlight: 'It's important to notice the equal emphasis [and which he means 'teaching' the technique to authors] given to both showing and telling: they each have their uses.'. A lot of writing sites are picking up on this recently, which is all good, it's just interesting to learn who said it first. Cogito said: Can I kindly disagree here. Showing shines through as much in a screenplay, radio drama etc as it does in third person narrative. Radio drama relies on dialogue (with some sound effects etc) but that dialogue will heavily utilise the same showing and telling techniques to hold the listener's attention. A reader will infer just as equally from what's said (the dialogue) as well as through what happens.
