Workprints often use placeholder music. Instead of Blake Neely’s final emotional/heroic score, you might hear temp tracks from major blockbuster films (like Man of Steel or The Dark Knight ). Some sound effects (whooshes, thunder) are missing or different.
That is an interesting find. The workprint for The Flash season 1, episode 1 ("City of Heroes") is a known artifact among fans of the Arrowverse. the flash s01e01 workprint
Some shots or cuts may be slightly longer or arranged differently. The opening sequence (Barry as a forensic scientist vs. the final reveal of the Reverse-Flash’s yellow suit) might be paced differently. Workprints often use placeholder music
Here’s what makes it significant: