I bought a Samantha Brown "carry-on" from QVC. I measured it and it seemed to fit the dimension test. Boarding a Delta flight last month, it simply did not fit into the overhead bin.
I don't think the pockets or expander zippers were used. With the help of a young man, I finally stuffed it into the bin, but checked it through on the return trip.
It was not a small aircraft so I don't know what was wrong. I've had much better luck with "smashable" fabric duffels (like the ones you can buy on cruise ships) - they are more pliable.
Hope this helps.