I'm only aware of comprehensive data for the USA, but see historical ceo-to-worker compensation. Note the extreme compensation explosion after the year 1994, which is shortly after the much more comprehensive executive compensation reporting rules were implemented (1992-1993).

Now, correlation isn't causation, but it would be a hell of a coincidence. Imho anyone who argues for salary ranges not being disclosed is trying to suppress wages. Whether deliberately or through ignorance.