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?
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.)