I don't know which country you live in, but in developed first world nations the manufacture and quality of Pharmaceuticals are tightly controlled and subject to strict government oversight. That isn't to say occasionally mistakes happen but this is rare.
I have long heard other drug users claim X brand of drug is underdosed or weak or something similar. The fact of the matter is the equipment used to manufacture tablets is tightly calibrated and not likely to make drastically underdosed tablets. If a company where regularly making tablets labelled as "15mg" but contained less, they would very quickly find themselves on the FDA's (or whatever drug regulatory agency your countries has) shit list.
What ive just said all makes perfect sense when you consider what's as stake. Some people require medicine to live and if a company was selling weak medicines this could be a serious public health issue. It's in the companies best interest to manufacture genuine correctly dosed medicine.
I'm not sure why you feel like these tablets are underdosed but I have a suspicion it's due to a bias of some sort. Our minds are powerful things. If I gave someone 10 Sandoz branded 5mg Diazepam and said "hey this Sandoz brand is weak! They're only really 2mg each" I would bet a substantial amount of money that they'd agree with me after taking them even though they are infact truly 5mg.
I reside in the sunshine state: FL, the endless

summer. I hold a bachelor of science degree in business from a major university, and was a VP at a large American based bank. So, yes, I do live in these United States. I agree with your perception of the American prescription drug industry. Why on earth would a company dare mfg a product it claims to be say 15 mg oxycodone, as in my illustration, and only put 3mg of oxycodone active ingredient? Most certainly as you alluded, government oversight and/or consumer watchdog groups would pick up from consumers, doctors who prescribe medications, etc , that a problem exists with oxycodone mfg by " company X", and the FDA, at minimum would initiate a probe, and send investigators to the physical plant that is mfg that product to immediately assess the product in question authenticity for purity, and it's adherence to the mfg guidelines that assure it is indeed making say 15mg unadulterated oxycodone pills. Afterwards, some of its pills would be studied by groups of scientists and random blind testing done, like you mentioned, giving say, one group of 10 patients 15mg of Rhodes oxy, and another group of ten people just a sugar pill, but telling them they are receiving a 15 mg oxycodone pill my Rhodes mfg.
Companies like Rhodes pharma mfg medication that people take for all sorts of diagnosis; some are taken by people whose daily lives depend on its performance , and any deviance in quality could put them at risk of an array of complications , even possible death. Compliance is a given in the United States, U.K. and as you mentioned in first world countries globally. You can't make a product and call it 15mg oxy, and put 3mg of oxy in it without getting caught. Not if you would be caught. Just when. It's inevitable. Personally, I have been in pain management since 2015 thereabouts, and have received oxycodone mfgd by many different companies. The mind as you said is a powerful "thing", no question about that. That's why they do these blind testing with 2 groups of people: one would get the "real" medicine as prescribed; the other group just a placebo, but told they indeed are getting the "real" medicine . In my approximately 10 years of being treated by different, highly educated, pain doctors, with my lower back being treated, I can most certainly, without a shadow of a doubt, tell you that 15mg oxycodone pills, by different mfgs, affect me/my pain level differently. Most of the time I have taken mallinkrodt 15 mg oxycodone pills. Other months I have received Kv tech ( K8 imprint) 15 mg pills. Both of which, within 15-20 minutes of taking one pill orally, turn off my lower back pain( which in intractable). Most recently,(Jan 2024) the pharmacy I have been using for the last several years to refill my monthly oxycodone, moved to a new location 60 miles north. Since their move, the DEA, suspended their ability to get most controlled meds, and ALL Schedule 2 meds, which includes oxycodone. So, I have been playing musical pharmacies since Jan 1st because of shortages of oxycodone, or pharmacy's restrictions on any new patients, or any number of reasons I've been told why they could not fill my monthly oxycodone prescription. I have been forced to look all over FL most months to find my meds, because some pharmacys told me they will fill my script, but only this one time because of restrictions. I have received these Rhodes pills only 3 times in my 10 years of being in pain management and twice this summer. I have compared the inactive ingredients between Rhodes and Mallinkrodt, and they differ. Accordingly I have been told by doctors, pharmacist, and others, that the active ingredient in all generic pills must be the same, but the inactive ingredients can vary. In my opinion, that's why the Rhodes 15 mg oxycodone pills do not work for me, nearly as well as others I have taken over 10 years. We touched on the mind, and how psychological things affect the way a pill may perform. The Rhodes pharma pills I'm sure meet all government, etc requirements, but, for me, and many many others, they don't give nearly the level of pain relief as others in the same category.