I am a newbie and looking at flight J2 016 for Aug 10 and looks like there are 12 business seats available (C6, Z4, A2) but the jet is an A319 with only 8 seats in business class. Then upon further investigation, this seems to be the norm, at least with J2. So what's going on here? Do they keep more than normal biz seats available and in case they sell out all 12, they swap the plane? Do all airlines do this?