In general I have too many razors in rotation to be able to tell you how many shaves I can get out of a blade before needing a refresh, however i recently went on holiday for three weeks and took one razor with me. At the end of the three weeks the razor is still shaving well. You hit on two of the things that can dull an edge quickly, the other I can think of is whiskers. I also wonder about how far you have pushed the edge. I have gotten the edge on a few razors refined too thin and they just don't last. They shave well to start and go down hill fairly quickly. That is also a possibility. When you go to refresh what does your edge look like with a loupe and how much do you have to put into getting our edge back.