Well, it does say in the previous patch that mines and mountains caps the purity of foraged minerals, but I assume that's just when you actually find a spot with high purity. Try comparing samples from boston with ones taken by an alt, see if there's any chance in the alchemical composition. Alternatively, ask someone to let you test a higher purity spot (that they're sure of) and compare to their results, or at least see if you can actually pick stuff above 1%

Exactly 6.022 x 10^23 worth of Lach molecules.