Yes, I noticed the same with my die no. 11. The same die number produces different headsizes. I do not know why but I noticed that the larger headsize also had a higher batch number (no. 4 for the 4.53 compared to 0 for the 4.52). (Batch no. is the number on the second line in front of the head size).
My guess is that the die wears during use and the higher the batch number the more it has worn out the larger the head size.
I was told by JSB that they do not make the dies aimed at a certain head size. But they make a die and determine the head size by measuring the pellet it produces afterwards.
It could also be that the headsize depends on the batch of lead that is used. There may be differences in crystalline structure of the lead between batches. Caused by differences in cooling, forming and stretching of the lead string. The one batch of lead may respond differently to the pressing in the die than the other resulting in slightly different headsizes.
Both my die 11 batches with the different headsizes 4.52 and 4.53 and batch numbers 0 and 4 shoot with the same good accuracy from the same rifle.