My '73 P has the extended screw bridge. Fender moved the bridge back about a half inch closer to the end of the Precision body for a while starting around '70 timeframe so the saddles may have had to extend further to intonate (depending on the setup of the individual instrument). When intonating with the bridge further back there would be enough screw length for the EAD saddles but the end of the intonation screw for the G saddle could wind up inside the saddle too far, hence the longer screw.
Since the P and J used the same bridge the long screw bridge carried over to the J.
Here's two pix I found at Chicago Music Exchange to demonstrate (note the position of the bridges relative to end of the body):
'69 P bass.............................................. .................................................. ......'71 P bass

