Yeah - that's a good pickup on the incorrect diagram. You must have a very detailed eye (or obsessed with blend circuit?
)
Still, they all work the same way. When in blend position of the switch, the neck pickup is in series with 15k resistor which is in turn in series with the blend pot. The center wipe of the blend pot is connected in parallel with the bridge pot before going to master volume.
Unless you're trying to make an exact copy of a particular '51, it doesn't matter how you wire it up (you can do it many different ways). But looks like you know which diagram is correct, anyhow.
WRT the 15k, you don't need it unless you want to keep the dark circuit (or unless you are building a replica).