From eMovie:
"In the 1930s and 1940s, a constant headache for theaters was being sure of having movie posters for their current releases. Often, the posters would travel with the actual film prints, and sometimes the theater before them might have forgotten to include the poster, it might have been defaced or torn, etc. If a theater didn't have posters, it was very frustrating! Several companies began in the 1930s (Leader Press, the "other company", Woolever Press, etc) that made posters of their own for new releases, and they would provide a back up for theaters in case they didn't get a studio issued poster. Often the posters from these companies (with the exception of the "other company") were silk-screen posters, but they were often quite attractive, and virtually always had a completely different design from the regular studio issued poster. It is a certainty that these posters were issued when the movies were first released. In fact, they were created PRIOR to the movie's release, so that they could serve as teaser or advance posters (theaters rarely got the studio issued posters before receiving the actual movie)."
&
"The "other company". This was a company in the Midwest that from roughly 1936 to roughly 1941 printed its own one-sheets and lobby card sets (and a very few inserts and half-sheets) for three major studio movies (Warner Brothers, Paramount and United Artists, but no other studios). The posters and lobby cards are from the original release of the movie, and almost always have completely different artwork from the regular studio release. They never have the name of the releasing studio on the poster or any of the lobby cards. Sometimes, "other company" posters or lobby cards have images that are the equal of those from the regular studio release posters or lobby cards!"