What Region are you in? Here in America (Region 1), they were released in trays wrapped in flimsy plastic. I think the clamshell sets were released in Region 2, but I don't know this for a fact.
sorry, not sure what I was smoking when I typed that. It's not clamshell. Flimsly plastic, yes. There is plastic sleeve, then the flimsy plastic pulls out with the trays inside. I'm in the US.