We had older tech parts that had physical fuses that could be observed with a microscope, and in fact, were observed with a microscope during wafer test to verify they had been properly burnt in. So what you're saying it's plausible. I've been out of semiconductor for about a decade so I'm hesitant to speak to something in a modern iPhone.

More interesting to me was how we would package the same part differently and sell it at different price points depending on how much functionality was brought out. You might decap a $10 part with X amount of I/O, cores, memory, etc and a $20 part with Y and find the exact same die. If the testing process was really sophisticated the $10 part would have a defect in the unused portion that made it more economical to down rate it than throw it away, but more often, it was just cheaper to maintain a single set of masks and sell the same die in multiple packages.