Never use imdb for tech specs. They are notoriously wrong or inaccurate especially for sound.
Most of the time you have to go by era produced and credits on end titles or original posters and the like.
Generally mono for most films before the late 70’s. Stereo and multichannel mixes existed for large format films and roadshow engagements.
Dolby Stereo matrix would get used Post Star Wars on most standard releases unless they cheaped out and stayed mono.