"Can you find me please a cast-iron definition of classical music?"
This one, From the Oxford English Reference Dictionary suits me as as well as any Steve:
"Classical Music n. serious or conventional music following long-established principles rather than a folk, jazz, or popular tradition. It is associated with acoustic instruments, in particular the orchestra, and the sonata form; however, modern experimental composers such as Karlheinz Stockhausen and John Cage, using electronic instruments and other devices, are generally considered to be working within classical music. The term is used more specifically with reference to music written c.1750-1800, as opposed to baroque and romantic music, and is exemplified by'-the work of Haydn, Mozart, and the young Beethoven. During this period the orchestra, the chamber group, and the various compositional forms such as symphony, concerto, and sonata became standardized."
If there are divergences from this, they are by sufficient numbers of people in agreement to make them contenders , which is not the case here, which amounts to a handful of folkies making a U.D.I. on their own behalf yet being unable to agree among themselves what they mean by "folk" or "tradition".
If the compiler can distinguish between other forms of music, as he/she does, why shouldn't we?
You appear not to wish to respond to my point - we are not being asked to accept another definition, but to abandon the one we have for nothing.
If you are prepared o do that, I am not.
If there is a wider meaning, what is it?
So far, the answer is the Humpty Dumpty one - "it is what I choos itr to be".
'54 is a bit of a red herring - I never use it other than to someone who wishes to delve deeper a starting point.
When these arguments started I had to drag down Bert Lloyd's book to remind me what it was - don't think I'd read it since I first bought the book in 1967   
Jim Carroll