I came across a fascinating website , filmsinfilms.com which features advertising for films within films. The advertised films are often, but not always, from the studio who made the film being viewed.
Henry Fonda in DAISY KENYON . The Greenwich is showing MR LUCKY and WOMAN IN THE WINDOW.
While Daisy KENYON is from Fox in 1947, the other two films are from RKO, 1943 and 1944.
From WOMAN ON THE RUN in 1950. The cinema is showing two other 1950 films, THE BIG LIFT and FORTUNES OF CAPTAIN BLOOD.
All three films from 1950 but three different studios, Universal, Fox and Columbia. So maybe sometimes it’s just an accident?
From WHITE HEAT. The Drive-In is showing SOUTH OF ST. LOUIS and SIREN OF ATLANTIS. All from 1949. One from Warner Brothers, one from Universal.
A nice touch from DREAM BOAT (1952) . Clifton Webb plays a former silent film star who resumes his career and stars in Sitting Pretty (which Webb had made in 1948. )
Fred Clark, Ginger Rogers, Clifton Webb (and Anne Francis in the row behind.)
From Phantom Lady (1944, Universal), SWISS MISS is from Hal Roach/MGM in 1938.
This wonderful marquee for Creature From The Black Lagoon (1954,Universal) was from The Seven Year Itch (Fox, 1955)