Earlier quoted context omitted.
At Apple's volume and level of system integration, it doesn't make sense to do assembly sharing at that level between different models. Presumably the SoC package is the same between the different products, but binned differently for the Air, Pro, and Mini. The actual logic boards would be custom to the form factor.
Not just that. At 5nm there will also be yield problems. I.e they will put the best yield into high end and the worst yield into low end.
I think what you are trying to refer to is frequency binning.