Suppose the *other* way is to add a second chapter to the one-shot, absorb it and continue writing. That’d get rid of the one shot vs big story issue. Because if it’s the exact same material/chapter in two separate stories… gotta tread carefully (site rules).
I suppose the better question is whether somebody can read & understand the spin-off w/o reading the one-shot. If there’s something crucial from that one-shot, a one-liner in the spin-off might be all that’s needed.
As I opened the long-story with them playing a game in it, I didn’t really explain the origins of it. Thus, nice tidbit to those that read the holiday story. To those that didn’t, well, still get entertained.
When I wrote Dale’s Game, it was “the continuation” to the holiday oneshot I wrote. Basically the oneshot explained where the gaming rig came from, the basics of the friendship, and the first chapter of the new story starts off with the boys using it.