In my experiences, the companions to get the baggage benne do not have to be in the same PNR.
My wife and daughters flew to Alaska last year from ATL, met wife's relatives there.
11 of us flying on at least 4 different PNRs.
MrsBHammy is also DM, so it got us past the eight - but they all had our baggage allowance.
Delta's website even says:
"The benefit extends on the Medallion Member’s reservation to a total of 8 travel companions, when traveling on a Delta-operated flight"
Companions, nothing about same reservation. As long as you have the same itinerary.
Last edited by BHammy; Feb 5, 2020 at 7:36 pm
Reason: added info