It's pretty straightforward, especially for the first 4 major levels:

- salary bands (+ stock awards & bonus. i.e "TC" bands)

- average seniority

- title change ( I (entry level) -> II -> Senior -> Principal -> ...)

- internal ladder descriptions (someone who worked at at least 2 FAANG companies can trivially figure out what maps to what, the titles & on-paper responsibilities are pretty standardized across most FAANG)