La boutique d'objets sur 14 septembre

Sometimes, and that is the pattern worth watching. Seasonal cosmetics — Halloween, Winterfest, Valentine's — cluster around their dates year after year, so a skin that appeared on this day in three different years has a decent chance of doing it again. Everything else rotates without a calendar.

Because the item shop only started in late 2017, and because a given date simply may not have had a notable rotation. An empty year is a fact about that day, not a gap in the data.

Yes — the full shop history lists every cosmetic ever sold, sorted by how long it has been gone, and it is searchable by name.