Here's the kind of thing that happened over the decades.
First, in 1908, an American composer (classically-trained and influenced by the structures of classical music), composes a tune he calls Moss Point Rag. It is published as piano sheet music, running to 6 sides of paper. Moss Point Rag comprises three sections in G, followed by a change of key to C for the fourth theme - the 'Trio’.
It is an attractive, merry piece of music, full of subtleties, syncopations, elaborate decorations of the melody and complexities:
At the same time, the early dance-bands and jazz-bands (with anything from three to ten musicians) are attracted by Moss Point Rag and want to play it. But they cannot possibly play it as written: the complexities you see in the music above are fair enough for a pianist’s fingers, but the melody-playing trumpet or cornet at the heart of the band could not be expected to cope with such melodies. Even a virtuoso player would soon be exhausted if he had to produce such a flow of notes (including many high ones) for a whole evening’s gig.
So the bands play Moss Point Rag in their own way. They simplify the melodies, sometimes using a cornet (or violin in the earliest days) with clarinet to do what they can to share the tricky bits. They capture the essence of the melody, rather than its many decorative notes. Some of them leave out the section called the 'Trio', because they find it less interesting or too difficult. They add a new section, either of their own invention or plagiarised from a different composition.
(For an example of this sort of thing happening, consider Hilarity Rag, composed by James Scott in 1910. To see the sheet music and hear how it sounded as a piano piece, CLICK HERE. But to hear how it was re-interpreted when a jazz band got hold of it, CLICK HERE. You see what I mean?)
In 1928, a band based in Chicago uses just the first two themes (much simplified) from Moss Point Rag, puts them into the key of Bb for convenience and records this version under a new name, Uptown Strut.
Towards the end of this period, a clever bandleader-arranger in New York records with his band a new tune called Spring Street Stomp but later researchers will find it is suspiciously similar to Moss Point Rag!
After the War, during the Bebop era, the tune is rarely heard in any form.
But twenty years later, in what has been called the New Orleans (or Dixieland) Revival, young traditional jazz bands again blossom in the USA, in Europe and in the rest of the world. A bandleader in England picks up the old 78rpm Chicago recording of Uptown Strut from 1928, works out his own version of it by ear and gets his band to record it. Many pub bands buy the record, like it and introduce it into their repertoire.
So the band (I’m now talking 1950 – 1965) plays its own version: each player has it in his head but the chances are that it is never written down.
The late Ray Foxley (he died in 2002) was the pianist in Ken Colyer’s band. Ray once told me he would learn tunes from those old 78 rpm records a few bars at a time – first listening and then working out the notes and chords on his piano.
Move on another 30 years and you find traditional jazz in decline again, though still with enough bands and enthusiasts throughout the world to keep it going as a minority art form. Uptown Strut is in their repertoire, with the composer usually credited as 'Anon' or 'Trad'.
Here are some of the old tunes still passed on from band to band in one form or another:
I doubt whether you could walk into a music shop today and buy the authentic printed original music for any of these. Please let me know if I'm wrong.