You seem to understand the significance of open dating, but for the benefit of anyone browsing this thread in the future:

- dated segment: protected to be routed on another carrier or routing if necessary, including credit for the mileage earned by the original booking (this may even be onto a non-OW carrier).

- open-dated segment: you are out of luck and must make own arrangements, including using more segments for a different routing. No protection for anything ... with open-dating you assume 100% of the risk.