It's total nonsense. He claims they are Word War I codes (for some reason I can't quite fathom) but then says it includes the word "Jerry", which was not commonly used until WW2. Lots of other incongruities as well suggest this is someone after their name in the paper, rather than a real solution.
As far as I understand it the message is not crypted but just
obscured with acronyms of plain phrases (PABLIZ = Panzer Attack Blitz). Young used a phrase book from WW I, which had phrases and acronyms similar to those in the pigeon message.
Not saying the paper is legit, but doesn't seem too unlikely to me that those phrases and acronyms didn't change much between the wars.
Can you point out the other incongruities you have found?
William Stott of the Lancashir Fusiliers was a private, never a paratrooper, and died fighting on the front. The Fusiliers are a line regiment, they had no airborne element.
There is no such thing as 'K' Sector Normandy.
He claims 27 1525/6 "translates" as 27/6 15:25 - which is rather a big leap, especially when you look at the actual message slip.
The message is laid out in standard one-time cipher style for the British Army at that time.
