If the fare rules show a routing thru CLE or EWR on a NW fare, it is a codeshare with CO. However, my experience has been, whenever you try to purchase such routing, Expedia will return an error message showing it cannot be priced.
If you are flying NW, go to nwa.com and book it. It will filter out connections on other carriers that only confuse matters. An e-ticket can be purchased without a service charge.
If you have a choice between 702 and the minimum 500 miles, the additional time on the ground and quicker connections may be worth the forgone 202 miles.