[Nick Beale]

An interesting story...

If the books don't agree with one another (and Johnson was probably relying on his memories rather than files, as with most pilots' memoirs) it seems that someone needs to check the Wing and Squadron Operations Record Books and any pilots' Sortie Reports that survive at the UK National Archives (which, AFAIK is what Chris Shores and Chris Thomas spent years doing for the new edition of 2nd TAF).

It's quite possible that even then the position won't be clear and that's where interpretation comes in. Even so, the source materials are the best bet for trying to work out which book is correct.