I have gotten zero PMs as well. I think rewording the heading might help, it might be leading people to believe that the spreadsheet is closed closed, like as in no longer being updated. I know it says differently but it could be taken different ways depending on how you read it(or if you even finish reading it lol). Perhaps just have it say PM so and so to be added/update your info.
Or it could just be the time of year, people are busy busy busy.
EDIT: Oh, the heading has already been changed. Carry on now...hahaha