it wouldn't be acceptable because it would be 3 more of the same exact game under a different title...
Not as separate games. I thought you meant those were possible titles for the prequel.
And I said it would be acceptable if the gameplay was different from the rest. If it's just another fnaf game then it would probably be stuff. If it ends up being its own game that tells the story of what happened before all the stuff started, then that would be okay.