As part of the QA on receiving heads from the manufactures, Titleist sorts them according to weight. If the runs of 7 irons were coming in a little light, as part of each set built, each head is brought to the weight tolerance specified. In your case, the weight was probably bumped to meet the weight tolerance. That the weight varies during casting/forging is not surprising. Maybe that Titleist does match heads to specified swing weights and otherwise adjust weight, loft, and lie for shafts, shaft lengths, and grip weights to tight tolerances is surprising.

Seeing the factory build each set one at a time and not just grab each completed iron from a stack to make a set was interesting to see.