To use it must you have at least 1 week that was purchased directly from Marriott. I have 5 weeks from the secondary sources and 1 week directly from Marriott. I was considering selling my last remaining Marriott week, but was told on a sales presentation that I would no longer be able to use the 13 month window if I did not have at least 1week purchased direclty from Marriott. Other sources have said this was not true. I am trying to get an official answer from Marriott in writing, but this is proceeding slowly. Anyone know if this is true or not.