Neodymium comes in many grades.
I have searched for 21,000 gauss NDFb but have only found 14,100 gauss. The reason is simple, I can't and don't know exactly how the magnets are aligned and what shape and polarity each magnet posesses. Furthermore, there's no way for me to tell whether the polarity is accurately set. Get your magnets together and use them in different combinations until you find the ones that give you the desired benefits. As far as the strength of the magnets are concerend, yes, there are variances among Neodymium too.