1971 seems to be the first edition,the above citation appears to be some kind of paraphrase of Ladybird's own text on the subject, which doesn't mention a date but has simply been assumed to be in correct chronological order.
www.ladybird.co.uk/aboutus/companyhistory.html
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Moon Girl Technologies horrendous beanbag, Tue 12 May 2009, 1:51,
archived)
so..the 60s then... ;p
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Azra3l Lubrication Persuasion and Brute Force ™, Tue 12 May 2009, 1:59,
archived)
by the skin of your teeth :D(
Moon Girl Technologies horrendous beanbag, Tue 12 May 2009, 2:00,
archived)