My wife(F/A) and I are considering booking a ZED on KLM from AMS to CPT soon. When you check KLM's website seat map for the flights in question there are several "classes" of economy(coach). When you buy a ZED fare on KLM are you limited to the lowest class of economy, or will they put you in an economy "premium" seat if they are unfilled? IOW, if the lowest class of economy has no seats will you be left on the jetway while the flight pulls out with economy "premium" seats left open?

Any help on this would be appreciated. Also, what is the best way to check the loads aside from checking KLM's website and attempting to buy a ticket in order to take a look at the seat map.

TIA...