Loki, I'm guessing here because I can't find either one of the couple of books I have on the DC-3.
American Airlines were the first to order an improved version of the DC-2 which they outfitted with 14 sleeping berths, calling it the DST - Douglas Sleeper Transport. This larger version of the aircraft had the door on the starboard side, for reasons I've forgotten. Somebody noticed that instead of 14 sleeper berths, the aircraft could be fitted with 21 day seats. This was the aircraft became the DC-3. That may have been the version that became the Li2.
