I think he made them all for 2 reasons:
1: People play and grind differently, so who was or wasn't pregnant by the time a player actually got around to tricker the 3-some would be unknown to Tinker, so better have all variations to be save?
2: Once made, it would be a lot easier to make the event repeatable later.
It's not the first game to have "not yet, or always, used pictures" in it's picture folder, so to base answers upon that.. might not be the best idea?
I noticed you wrote earlier that you can't play the game on your laptop atm, so you could not test your saves in-game to find what trickered the debated 3-some as a repeatable event. Also there are like 3 months between each new game version, so it's likely you could remember wrong about seeing it repeated, maybe you saw it twice from a reload of a save to indeed see the different pregnant variations made?
I'm gonna trust the discord msg from the Dev on this one, that the event was not made repeatable yet