Alright so, this is going to take great leaps of logic but hopefully it will make it easier to pinpoint exactly when he got trapped in Spring Bonnie.
So, for me I think he gets trapped and killed within the suit a LOT closer to FNaF 3, if you want to get more specific, if we assume FNaF 1 takes place around 1990-1994 and FNaF 3 takes place around 2020-2024, he would have died around 2015-2019.
Let's look at some evidence to support this:
Springtrap has a relatively-new looking corpse inside him, human flesh, veins, guts and some organs can be found within him, which means a lot of his body hasn't decomposed yet, the actual exact point of reference we can take from a part of his corpse can be his eyes. Those eyes aren't animatronic eyes, they are human eyes (I will provide reasons as to why if you want), human eyeballs take around 4 to 5 years to completely decompose, and those things still look fine, this would mean that he had to have died some years before the game started.
The Between-night minigames show a MUCH, MUCH decrepit version of the FNaF 1 restaurant, you can't really see it at first glance, but the Purple Guy broke into the restaurant A LONG TIME after it closed down. The animatronics are BEARELYgiggle functional, their servos have been rusted to a point that they can barely move, and that the Purple Guy can easily dismantle them when he gets the upper hand on them, just look at Foxy, who can't run like he used to in FNaF 1. The place is full of rats, filled with wholes on the roof that water can come through, everything is old and left to rot.
Why would the Purple Guy break into the restaurant after DECADES of it being closed?, my guess is that he heard that some guys in a theme park were going to be buying the property and looking around to salvage the animatronic parts and objects from the pizzeria, to open up FAZBEAR'S FRIGHT. So, to keep anyone from finding evidence to incriminate him, or because he didn't want those guys to get a hold of the animatronics (because they are KILLING MACHINES), he goes one last time into the Pizzeria and destroys them, and getting himself killed in the process.
Alsoyoustillhaven'tletmein2124youbutt...