My brother-in-law works in pharma manufacturing, this stuff is really hard and it's basically impossible to create exactly identical pills, apparently in large part because the active ingredient is frequently <1% of the volume of the pill. The best they can do is control the range of dosage in pills, and there's variance in what that range is across drugs (i.e. some compounds can't be spray dried, can't be heated hot enough to make binders liquid, etc).

Depending on necessity and value they can typically engineer more precision, but it gets very expensive very fast.