Thanks for the update!
It seems to preserve the dates and flights but not so much fare codes.
e.g. I tried this itinerary
Itinerary
Newark (EWR) to Athens (ATH) — Tue, May 14
Newark (EWR) to Oslo (OSL) — Tue, May 14
Scandinavian Airlines 908
Dep: 6:50 pm
Arr: 8:15 am
7h 25m
Airbus A330
Premium economy (P)
Meal
Layover in OSL
Wed, May 15
22h 35m
Oslo (OSL) to Athens (ATH) — Thu, May 16
Scandinavian Airlines 4637
Dep: 6:50 am
Arr: 11:40 am
3h 50m
Airbus A320neo
Premium economy (P)
Meal
Athens (ATH) to Newark (EWR) — Tue, May 21
Athens (ATH) to Copenhagen (CPH) — Tue, May 21
Scandinavian Airlines 778
Dep: 2:50 pm
Arr: 5:10 pm
3h 20m
Airbus A320neo
Economy (R)
Refreshments for Purchase
OPERATED BY SAS CONNECT
Layover in CPH
1h 5m
Copenhagen (CPH) to Newark (EWR) — Tue, May 21
Scandinavian Airlines 901
Dep: 6:15 pm
Arr: 9:05 pm
8h 50m
Airbus A321neo
Economy (R)
Meal
Priceline kept the flights but dumped them all into economy instead of PE. For SAS, it does support upgrading the itinerary to PE, but then forces you to do it for both legs instead of just the outbound as in the original.
SAS website lets you do it but then won't offer the option of a 22-hour layover. Since their site won't let you book multi-city itineraries either, there's literally no place that will let you book this yourself.