How to update drop lists in Excel?

the instructions here do not seem to apply to the Conference Planning Checklist. I followed the instructions, and 1) it would not allow me to enter the new name in the order I wanted it inserted, and 2) it did it for only that cell, even though I checked the box that said do it in all simliar formulas.  Have I overlooked some additional instructions that were given, or was this instructional video not complete?