So it's come to my attention by an associate of mine that the original Friedrich robots aren't the same as the ones Alan tries to survive against. While they did say that this was confirmed by Ryon, I think that's stupid so here my rebuttal:

Bernard's older model clearly has stitches going through his face, implying that even the older model is made out of felt. The wires between each of Bernard's body parts are also visible, which implies that the innards of all these animatronics are wires.

Now, here's where my theory starts: it's seen in the mini-games that the Friedrich fellas really hate the technicians, brutalizing them and turning them into pizza. My theory (it's more like head cannon) is that as the many years have gone by, the Friedrich crew has repeatedly butchered the various technicians and taken their innards.

What would motivate them to do this exactly? Well I think Goldenfriedrich is the one who inspired them to start stealing organs and shit. Ryon has explained that Goldenfriedrich has always wanted to make his own animatronics, so maybe he attempted to stuff dead engineers into the original robots? It's a stretch, and I'm not sure why the animatronics would start doing it themselves. But I'm still confident in this theory for three main reasons.

1. It explains why Goldie taunted Alan by saying "YOU KNOW WHAT THEY'RE MADE OF". Implying Alan has seen what made the animatronics so unusual.

2. It explains why the animatronics kill the technicians. Beyond just "because they're bored" at least, this give some motivation behind the murder of Mario Brother (rest in pasta). Also, this ties back into the first reason.

3. Why Bernard is SO JACKED. You think the flesh inside this guy came from nowhere? Nah he 100% took it from the Technicians to become so beefed.

So that's the theory, and I know that this is technically pointless because it's been confirmed to be false. But fuck it, confirming it outright is boring as hell, I vote that whether the old animatronics are different to the new ones be completely ambiguous. After all, there's really no need to confirm this detail, and confirming it outright kind of just kills all discussion.

(Edit: Ryon has confirmed that it's ambiguous)