Imagine like a FNAF x FNAC crossover whereas Fazbear Entertainment buys CTC entertainment/the right to the characters and rebuilds the fnac characters. They rebuild Candy, Cindy, Chester, and Blank with updated program like with the FNAF characters.
They consider rebuilding Old Candy, since he existed during the 1980s era, but hold off because he was put out of service for harming an adult during hours. Anyways, the 'new' CTC animatronics would have the same AI as say the SB animatronics, having their own conscious and stuff, and putting say something like that inside Old Candy, he would lore drop about the incident, as well as other nod backs to his time in service.
Well, realistically this *could* happen since fnac is cannon in the fnaf universe, just not how I'm picturing it..