they still could be worn out. I sharpen grizzlies and I can tell you with chalking I wear out a file in about five to six months.
I do sharpen all year long, and do it every time I hunt...and sharpen heads for visitors to the camp, so obviously mine get more use and are used on harder steel than many broadheads, so your mileage may vary...but if you haven't chalked, and have clogged them up, they could be worn out and need replacing.
I use box call chalk as well. I think soapstone would be awesome and hadn't thought of that. Good idea guys.