The Mozzies don't vary as much in weight as most pellets (5% with Mozzies , 10% with most others)
but there is variation between batches and tins.
I think it's to be expected that as the dies get older they produce lower quality pellets and I guess that applies to all makes.
I noticed with the Mozzies that there are three distinct skirt finishes;
1# Skirt is solid straight, clean and even.
2# Skirt has a small ridge/burr/lip on the inside edge
3# Skirt has a larger ridge/burr/lip on the inside edge
My guess is that your 1st and best batch has no deformation and is type 1
Type 2 are ok, type 3 groups are poor.
I have found tins with both type 1 and 2 in the same tin.
Anschutz 2013 MEC1 .22LR
Miroku 3800 12bore