Originally Posted by
WidgetTravels
On Delta flights, it's very rare to be able to buy a seat and not use SkyMiles. It happens occasionally, but very rarely.
Delta can't force partners to make seats available.
No...It's not "very rare". I find it happens with frequency when the overwater segment is on DL but the intra (e.g.) euro segment is on a partner. The partner segment is available but DL's married segment logic screws up and acts like the entire itinerary isn't available.