Just Remember that FNAF 4 shows the mangle, which only existed n 1987, and everything will be fine.

I think I can explain the newer animatronics showing up earlier than they should.

This is the 80s, a decade known for having a ton of cartoons soley to sell products to kids. GI Joe, Transformers, Carebears all were created to sell toys. Fredbear and Friends is clearly one of those kinds of shows. They are there to sell Toys and promote the resteraunt. So when the show wanted new products to sell, they simply added a character too the show. Sure they didn't have a matching animatronic but they could still sell the toys.

After this site closed down they reused the old ideas for new animatronics.