I don't think they knew exactly how many sets were affected. My theory? As I mentioned a couple of posts ago T&Bs have magnetic slugs and I think they got the polarity the wrong way round. Usually slugs are just cold rolled steel so their orientation doesn't matter. As these are different, I wonder if they weren't labelled up properly and/or not labelled at all so they got thrown into pickups any which way.
If the QC test just checks the DC resistance all looks fine and they get shipped out. It's only when you install them in a guitar you realise there's a problem.
There's been no issue with an exchange, so it's been a bit of hassle uninstalling them and re installing new ones but it'll be sorted in the end. Everyone makes mistakes, but as BKP know it's how you deal with customers that's important!