If the parts were actually useless, they would've been trashed. The fact that they were sold and used is proof that they weren't useless.
Not that unscrupulous sellers don't exist either, but again, see above. When there are regulatory forces in place to prevent that, you get a well functioning market.
There's plenty of history of this, of actually trashing parts that don't meet spec. Manufacturers aren't afraid to do it. There are plenty of photos of, for example, mounds of finished vacuum tubes, to be crushed and disposed of (or hopefully recycled?). Selling dysfunctional parts would be more harmful to their reputation than the value of those parts, even if sold through appropriate channels (or indeed, the cost of setting up that "budget"/off-spec/relabel sales channel wouldn't be worth its revenues).
A better concern would be if they were reliable, at whatever capacity they had. I don't know about the chips in question, but it's generally the case that semiconductors don't change much over time (aside from exposure to ESD, which is avoidable in finished products by appropriate design). It's a good guess that, within that available capacity, they're fine, functionally indistinguishable from a chip of the same (design) size. That is, the defect happens to cause a few memory bits, or cells, or decoders or whatever, to malfunction, but the rest of the chip is and shall remain perfectly functional aside from that.
I don't know what's difficult about understanding that.
It's like I sold you a car that, by all indication is supposed to have a 4-cylinder engine in it, but I actually put in a V8, but I did a shitty job tuning it so it only makes the power of a 4-cylinder anyway (and yes, assuming other circumstances are comparable, like equal mileage -- maybe it's just not getting enough fuel or something, so it's somehow just as efficient, but only delivers half max power). And you're complaining that I've somehow defrauded you, but you're getting a car exactly as described.
Tim