Originally Posted by ND76

Often, the standbys are Delta employees flying NRSA (non-revenue). They would get the open seats in C+ (non-medallion paying pax are in the back unless the flight is oversold or are in an IRROPS situation). This is why you can't count on a middle seat in C+ going out empty; at the last moment, DL will give that seat to an NRSA standby who wasn't on any gate display standby list).