For the cheapos I got 25, for the Bourns I got 27... meaning about 2/3 of the cheapos were within 25 of 500K...
That's a tolerance of around 5%. That's pretty dang good. A general standard amongst mfr's is up to 20%! And some will charge a premium for under 10%. I reckon you've done pretty good fender3x!

Alphas don't get much love here, but they have spec'd fine when I have tested them. I have a bunch (just not in 500K) and they are used by lots of top MFGs.
I've had very good luck with Alpha. I will say that there are *good* Alpha and crap Alpha models though. The ones that Jaycar sells just feel chintzy. I've never used those in a guitar. The ones I've bought from guitar parts sellers have been just fine.