Many people utilize either IMDB or TCM as their research tools for determining the intended widescreen theatrical aspect ratio. As the recent discussion of PLAN NINE FROM OUTER SPACE illustrates, these sites are not always accurate.
To determine the correct aspect ratio (the one intended by the director and cinematographer while composing each shot) you have to look at the studio policy and date of production.
I've been doing this research since 1990 and have been able to accurately document the intended ratio of all fifty 3-D features from the 1950's. I believe in doing original research with documented, primary source materials and have gone through hundreds of industry trade journals (Boxoffice, Variety, Hollywood Reporter, American Cinematographer, Exhibitor, Motion Picture Herald, etc) as well as studio documents such as Daily Production Reports and minutes of the Daily Committee Meetings at the various studios. From this research, I've been able to accurately determine when the various studios switched over to widescreen cinematography.
Paramount was the first major studio to go 100% widescreen (1.66:1 was their house ratio) on March 24, 1953.
As an example of the wrong information found on those sites, I present the following:
Title and Studio - IMDB listing - TCM listing - Director/Studio Intended Theatrical Aspect Ratio
MISS SADIE THOMPSON - Columbia - 1.75 - 1.37 - 1.85
MONEY FROM HOME - Paramount - 1.75 - 1.37 - 1.37
THE GLASS WEB - Universal-International - 1.37 - 1.37 - 2:1
DIAL M FOR MURDER - Warner Bros. - 1.37 - 1.37 - 1.85
GOG - United Artists - 1.66 - 1.37 - 1.85
JIVARO - Paramount - 1.85 - 1.85 - 1.66
TOP BANANA - United Artists - 1.37 - 1.37 - 1.85