I think it depends on which edition of a particular set and/or when it was made. Some of my Mill Creek collections are single sided and some are double sided. It seems the older versions come in thin cardstock outer boxes and are double sided, and the more recent ones are in harder plastic...
I find it difficult to keep track of the PD megapacks, every so often it seems I come across one that I didn't know existed but that has been out for years. Are there any glaring exceptions to the following list:
150 episode Westerns (4 different)
150 episode Detectives
150 episode Family TV
150...