You should ALWAYS have returned it as defective, regardless of what the manufacturer reckons; depending on your local consumer protection laws, of course.
You would never expect to roll a new car off the lot with a flat tyre. Why would you expect a screen to be ok when the main part is glaringly defective? .
The short answer is there an ISO standard, ISO 13406-2 for LCD displays; pretty much every display is sold as a class II. A guaranteed defect free display (class I) is a premium product. Shops have sold 'seconds', products with minor imperfections since forever.
So, especially back when defects were relatively common, I reckon your case is fairly thin, although jurisdictions will vary. Now, when expectations are higher, maybe that's changed.