The "last batch" is really relative to when you bought it and how long it was on the self. I have noticed that my most recent box has a higher Mg (1350) been and a tad lower alk (10 instead of 11).
I've been getting around 160ppm Alk and 420 Calc with mine... just got a new box and mixed in a bag with the little bit I still had in the bucket and same parms. My Mg always runs high with it though around 1530 with salifert kit. I mix to 1.026 measuring with a refractometer. I was getting around 200 ppm Alk / 450 Ca around same Mg. I test Alk and Ca with Hanna checkers.
I haven't tested the parms but I just noticed what I thought was a difference when I poured it out of the bags into the bucket and when I was measuring it. Seemed to be more "fluffy".
Yes. when I pour the salt in a 5 gal. of heated R/O water with a powerhead for mixing. the top of the water looks like it's smoking for a minute or so. and I noticed my ALK being lower in my tank. I have not tested the fresh salt water yet. I thought something seemed different.