Patience, please. I'm new here!

On my last day of free trial of Expert Flyer and I see lots of interesting data - M fares with Z availability and even the magical S available on flights that I want...

BUT I cannot for the life of me cause them to come up on delta.com (or 3rd party booking sites). If I advanced search for M or higher, I always get B; search for S and get at least I - and usually higher than that.

Have played with searches, dates, routings, etc (you know - the way you'd do it *without* all the insight!) and can't get a hit.

Is there some trick to getting DL to sell me the seat that EF tells me is available?