difficult? just need an open seat. expensive? well jfk-fra on lufthansa shows $75.31. on Delta it shows $94.78.

Delta is always more expensive because they value themselves higher than other airlines, apparently, and charge zm instead of zl. or maybe even zh. those prices are for JetBlue employee. I didn't check parent or spouse or whatever.

every agreement is different. my mom and I can fly zed fare on all Nippon, but not my girlfriend (travel benefit domestic partner). and the opposite is true for some other airline that I forget. some charge zl (zed low) for parents, some zh (zed high) and then zm (zed medium) for spouses or kids or something.

it is all over the place. we do not have zed agreements with every airline. that's for sure. many Asian carriers, for example. there are a lot on the list, but there are quite a few missing. maybe it is the same at other airlines, I don't know.