I have to think it's a mistake, because a lot of them just don't make sense. You'd think they would be based on the "First release date" field, but then why does Aliens: CM say Q1 2013, which is for the Wii U version, instead of February 12? Omerta also says Q1 2013 (the date for the Mac version), and P4 Arena says 2012 (the date for the UK 360 release). And then The Walking Dead and Fallout 3 just say "N/A".
It's like if any one release has a fuzzy date/no date, that's what shows up.