You see this in lots of long-play shows/properties. Adventure Time comes to mind. A number of seemingly irrelevant details become central to the main plot in much later episodes (years/seasons later).

I am wondering, however, whether there is some sort of plot bible that lives with the “keepers” of the storyline, or whether some details are just randomly sprinkled here and there as hooks with the hope that writers will weave them into the future plot.

Either way, this type of writing is extremely rewarding to long-time fans of a show.