I think I figured out how to make re-order dates work in orgmode. The start date is the date when items start getting used. So subtract the number of weeks before the next order is needed from the start date and write that time stamp in with a + repeater value to cover the days until the next order. You get back your start date with a repeater. So copy that time stamp down and so long as the repeater continues to work you should get a series of dates matching your re-order date requirements. There may be an easier way to do this in orgmode but I haven't run across that one yet.
