That doesn't tell me why you can't ask the players before you begin those months of work.
Are you actually investing that amount of time and energy before you know who is going to play the thing? If so... you must have way more spare time than I do.
While not the intended, I've also done that.
Recently even. I've prepped for 4 systems recently - but am using 2 of them.
Prepped: Stargate, Talisman Adventures, Cortex Prime, and Twilight 2000.
I've got some players for EACH of those, but only Stargate and Talisman are hitting the table. Both groups want me to run Pendragon again... but I'm not ready for Pendragon - but if my players decide as a group to go to it, I can be ready in a week. 3 Weeks if they insist on a different edition than 4th.
My friday group has asked for Star Wars, Star Trek (but not Modiphius'), or Firefly... But I think Talisman for them is more suitable for me to put adventures out there. When
My sunday group is playing Stargate
Vaesen is going away not because I don't like it, but because I'm not comfortable running it with my own adventures (and the 4th adventure in the book just fails to capture me). My friday group is not prone to subtlety. So, we finish the adventure, and move on to Talisman.
Stargate is limited run. I've an end point, after which I plan to migrate the sunday group to their choice of T2K4, Pendragon, Talisman, or a homebrew in Cortext Prime, or, just maybe, Burning Empires.
Some of my prep is done on each of those. None of them is quite ready besides Talisman.