Another thing, I was playing bass at that time and remember when the 3 bolt neck became popular. That was a very bad time for Fender as neck pockets suffered from being cut poorly. Most new basses were returns for a multitude of problems like howling electronics, shifting necks, bad intonation amongst other things. I was told this while sitting in Sam Ash trying out basses to buy. This is probably the reason the 4 bolt to 3 bolt conversion took so long, it took some years to get it right and people knew this so they wanted the 4 bolt necks instead!