Both documents approve the same police contract instrument (June 2010–May 2012); Document B is the adopted/final form clarifying the contract term after Document A's initial approval.
Document B (Nov 2010) is the original police contract approval; Document A (Apr 2011, 171 days later) approves a revised version of that same contract—two separate board actions on the same underlying instrument, not a literal revision of one document.
Recurring pattern
These other chains use the same template but are separate decisions: