Rather than hi-jack the interesting, related thread on damping strings, I thought I would open this one solely on the topic.
What I know: Precision basses, when they came from the factory in the late 1950s and early 1960s, had metal covers over the bridge and pick-ups - the two shiny gold pieces over the strings seen in this photo. Turned upside down, they looked like ashtrays, which is what they were often called. Most guitarists removed the covers because they limited access to the strings, and Fender in later years, yielding to the market, deleted the covers.
But did our hero bass guitarists from the period - Jet Harris of the Shadows and Nokie Edwards of the Ventures – record their greatest hits with the covers on? Did they remove them at some point, and if so when? When did Fender delete the covers?