It is terminology and the key word is "some". The processors did not perform up to specs. That's why they disabled the cores. It wasn't 1 core that made the chip not pass. Disabling 1 core made it a tri-core that passed the 720 minimum specs. It does not mean they are defective but we are talking in words. If they work, they are not defective. Plain and simple.
Intel did something similar years ago. At this point, I am not saying they are or are not defective. Its an interpretation but if you unlock the 4th core and it works does that mean it was defective? Nope! when they tested them at AMD and they did not pass specs, they disable a core thus making it a tri-core. In most cases the 4th core works. Again is it defective???? Nope, maybe it wouldn't clock at the spec core frequency, but when they lock the 4th core it did. So saying this, unlocking the 4th works at least 90% of the time if not more.
It really is not worthless information. I fully read the explanation years ago when AMD first did this and someone "labelled" them as defective but as you attest, some are not defective!
I got an unlucky 940. Mine barely is stable at 3.7GHz(while others get higher). I cannot get higher but the chip passed the minimum spec for 940 so they released it as a 940. Chips that do not pass min requirements as advertised are thrown as a 720 tri core with 1 core locked. This does not mean the core is defective, it means the chip did not pass min req. advertised frequency. Again, the 4th core works and it is not defective.
Anytime you disable a core, you can clock the chip much higher. I locked 2 cores on my 940 and clocked it to 3.91GHz stable. I guess I have a 550 now? LOL but my 4 cores are not defective.
With all this in mind, someone at AMD made a great strategy. Instead of wasting those chips, they did what was explained above and saved the company a lot of money or maybe I should say made the company a lot more $ with these subpar chips. Some actually overclock very nicely and hang with the 940 with the 4th core enabled.
In closing you are WRONG.
In my background section, I think I explained things broad enough so that both you and Dopamine are correct. Let us leave it at that. SOME processors have defective cores, and others have cores which were disabled to meet market demands. Regardless, they were disabled for a reason. Broadly speaking, they did not meet AMD's quality control specifications for reasons unknown to the public. Since we have no method of determining which chips have defective cores, I will continue to use the term "defective" to encompass the disabled cores as well.