I think the evidence is that Gibson headstocks break a lot, and I don't see evidence that banjo peg headstocks were stronger or broke less often. In terms of numbers made, I would venture that the percentage of 50s Gibson basses with headstock breaks is higher or at least as high as later models. For a cause besides dogs or people knocking them over, the banjo pegs suffered a lot of damage when cases got lost or tossed. A 50s EB, EB2 and EB0 came with a case that had a higher neck block. When a 50s bass gets stuck in a later EB-fitting case the headstock actually rests on the pegs themselves. Lots of breaks from that alone. This became a bigger problem in the 70s for instance when a 50s brown case was worth more than the EB-2 or EB-0 inside, so the ES-335 and Les Paul vintage fans were buying them for the case, then selling the bass for the $150 or so that they were worth top dollar into the mid 80's.