Interesting! I've never heard about this. The Yamaha website still says 40 mm (= 1.575") for ALL their 4-string BB-models. Where did you get 1.59" from???
I purchased my BBP34 brand new around 4 years ago (I'm not sure about the actual year it was built but definitely older than March 2023). The width at the nut measures 1.578", which is pretty much spot on 40 mm.
1.5" would definitely be a noticeable difference (almost 2 mm), and not necessarily for the better, depending on personal taste of course. This would mean moving from a neck that's leaning heavily towards a slim/"modern" P-bass neck to a J-bass neck. When necks get slimmer I generally like them to also get thicker front-to-back. I'm not sure I would be as happy with a 1.5" nut width unless they also make the neck profile slightly "deeper" (which is suspect isn't be the case here).
Can anyone else with a BBP34 (or other BBs for that matter) made after or around March 2023 confirm this?
I meant 1.57" per the Yamaha secs... I did run across a new BBP34 at an online store & they said the nut width was 1.59! It was built in 2-2023. So who knows!