Out of all of the original animatronics, Withered Freddy seems to be the least damaged, with only a few tears through his body.
In-game, according to Phone Guy on Night 2, it is explained that he has gone through an attempted retrofit, but was left unfinished after the management chose to make Toy Freddy (much like the other original animatronics being replaced by their respective counterparts).[1]

His overall appearance is unchanged, but small differences are visible - mainly the buttons added