Yes, this is important. The doctor will use a rule of thumb at the very least to prescribe a certain dose, or a dose within a defined range, say for body weight, or maybe for age, even for sex, and in concert with other drugs prescribed that the patient ought to be taking routinely. So, if a generic brand fails to provide the relief or remediation that is intended in the prescription, the prescribing physician MUST BE apprised of that result. If nothing else, this is an ethical orientation to other patients who are also relying on the drug, and who may also not be deriving the intended, even life-saving, benefit. The company purporting to back their product needs to know, or to be sanctioned, even prevented from selling their product. It's what the FDA is meant to do for Americans.