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.