Stamp Grading - Of Value To You Or A Marketing Ploy?

Not really ikey. They're typically interchangeable, although connotations exist in-line with what you stated. It will lead to confusion.
In my car, if the airbag is faulty it could be due to a manufacturing defect. The reason for fault is irrelevant unless asked upon.

Also time of sale, is less relevant. If you were to split hairs, I might differentiate with production vs. use fault. Getting a little more pedantic - Production faults can be good, while distribution faults are nearly always bad, with the exception being things like rare usage (cancels that improve value for instance).