DL is notorious for one-stop flights that almost always have a change of equipment in ATL (with a walk from gate A1 to B39, per Murphy's Law). AA does this sometimes, but usually when AA offers a one-stop flight on a domestic city pair, they mean one stop on the same aircraft.

Piedmont often assigned a single flight number to a routing AAA-BBB-CCC-AAA. The BBB-CCC leg of flight NNN would have some pax traveling BBB-CCC, others traveling AAA-CCC, and still others traveling BBB-AAA. This led to some interesting flight lineups on monitors too.