Hey everyone! I am here with another theory! This one is about well... Look at the title! Anyways, let's get started.
So first, I just wanted to clear something up, Golden Freddy IS Springlock too. Phone Guy in FNaF 3 mentions the company has TWO Springlock suits. What is a common aspect in SpringTrap and Golden Freddy? They are both yellow. Maybe that could be a way new employees differ wearable from dangerous suits.
Halfway through FNaF 3, Phone Guy mentions an incident involving the spring locks failing in a suit (Purple Guy's death). Because of this, the Springlock suits were taken in for repairs, while 2 Temporary suits would be used while the repairs were underway.
What importantance do these 2 replacement suits have? They are Shadow Bonnie and Shadow Freddy. Why? Well, both appear black with glowing white teeth in FNaF 2, but revealed to be purple in the Minigames. Purple Guy has been shown to wear the Shadow Freddy suit. Also, since they are both purple, perhaps purple could be a sign for new employees like yellow is for the normal suits.
Also, notice which characters they are? They are alternative versions of Bonnie (Well, technically Toy Bonnie.) and Freddy. Golden Freddy obviously equals Freddy, and SpringTrap is called Spring Bonnie by phone guy. The parallels of both Shadow Freddy and Golden Freddy being Freddy counterparts, and the same with SpringTrap and Shadow Bonnie being alternate Bonnies also points at the Shadows being the replacement suits.
Finally, Shadow Bonnie and Shadow Freddy seem out of place and to scary to actually be in a kid's resteraunt right? Well, yes that IS right. But, Phone Guy says that the suits could be seen as inappropriate/irrevalent, and that questions about these aspects should be ignored.