We can access current privilege policies from http://stackoverflow.com/help/privileges. However, changes to the policies are not documented there. There has been at least one notable change - the requirement to access review queues was increased from 125 to 500 reputation. How can historical data on privileges be accessed?
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Internet Archive to the rescue!
(Note that "access review queues" wasn't a concrete privilege for a long time, and /review doesn't give much indication when you're not logged in (the Archive-bot isn't) - you'll need to find those elsewhere, e.g. on Meta.)