You're right, of course. It makes perfect sense. I was just trying to justify why a GP wouldn't order a glucose tolerance test on a normalised HbA1c diabetic. If what you say is true, then maybe they should.
The usual reason - cost. An OGTT takes a minimum of 2 hours and requires nurse time to do the finger pricks and administer the drinks. They also have to be fasting, so early morning appointments are necessary, which makes it harder to fit appointments in.
Rather than an OGTT it would be more sensible to do an insulin test on all T2s, and certainly before they are given meds like Gliclazide or insulin. (which can make matters considerable worse if the pancreatic insulin is already high) But .... it doesn't happen.