The memory is not on-die, it’s separate (completely standard) memory chips, either DDR4 or DDR5 depending on which M-series CPU you’re looking at. So binning doesn’t really apply.
Seems like there's a misunderstanding on my part here. <reads more>
Ah, the memory is integrated in the same package (the "chip" that gets soldered onto the motherboard) as the integrated CPU/GPU, and I had understood that correctly. However, I had incorrectly surmised that it was built into the same silicon die.
Thanks for the correction!
Lesson: TIL about the difference between System-In-a-Package (SIP) and System-On-a-Chip, and how I had misunderstood the Apple Silicon M series processors to be SoCs when they're SiPs.
No worries! It’s made more difficult to understand by 1) Apple’s marketing, which does a great job of tricking people into thinking that the memory is actually integrated into the die without actually saying so, and 2) the fast-and-loose use of the SoC and SiP terms, which are often used interchangeably, including by Apple in official marketing materials [1].