There doesn't appear to be any easy way to discern the game id using the date, teams involved, previous id, etc. You'll have to scrape these values from some other page.
that is for game on november 8th 2012, so lets say i want a game in 2011 it would make sense to lower the number... if i change the 4 or a 2 to a 1 i get a blank page, so would be helpful to know how they use those gameIDs
espn is generally not a very good source for boxscore data for baseball(check out retrosheet or fangraphs)... i only know about the boxscores because i wrote a script to download the latest scores (used to auto grade bets)