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I don't know how Google does their salary, but a lot of big corps do salary bands by level, and when the 2x a year (one of which might not be advertised) company adjustments come up, they determine merit based rases and then adjust to try to tighten the bands. So if you're underpaid, you'll probably get a bigger raise than otherwise and if you're overpaid, your raise will be adjusted down.

You might not ever catch up to someone who started higher (and certainly won't for the integral of compensation), but the gap should narrow over time.