This is normal. Always take new measurements every new box even if lot # is the same. Usually (most of the time) once you find the proper seating depth (in relation to the lands) it should hold true for different lot numbers as well. There are always exceptions so beware.

If the 105 Hornady BTHP shoot best in your barrel jumping 0.030" then other lot #'s of same bullet should too.

Thus having to take new measurements every new box and re-adjusting the seating die if necessary.