Always best to just look at DL's rules as they are now, rather than rely on what happened to somebody else somewhere else at some time in the past. OP's connection is between 6 and 8 hours, so he may but need not reclaim his bags at ATL.

Rule 116(2)(a) Connection Time Exceeding Four Hours
Passengers making connections to the first available Delta flight departing from an intermediate point may reclaim their baggage at the intermediate point if the connection exceeds six hours, but is less than twelve hours. If the connection time exceeds twelve hours, the passenger must reclaim his baggage at the intermediate point.