Joseph Campbell didn't invent the Hero's Journey. It is a story structure pattern that has been repeated since long before his time and can be traced back to early Mesopotamia.
Campbell is simply the latest person whose labels have become common currency.
There are two easy-to-use evidences:
a) An analysis of any successeful story since before his time reveals the pattern. Therefore the makers of those stories films knew the pattern (Casablanca (1942) is decostructred below).
b) You cannot write an effective story simply by using Campbell's structure. Knowledge many more structural elements is required by screenwriters.
? Meeting with the Supernatural Aid Mentor and receiving a Magical Gift [Rick meets Ugarte Wholesale Jeff Teague Jersey , who gives him the Letters of Transit].
? Hero Tested. Rick given the chance to sell the caf? and leave with the Letters of Transit [Ferrari offers to buy the caf?]; Loyalty of Allies Tested [Sam won't leave despite the salary rise offered to him].
? Hero's Inner Challenge demonstrated [Rick cannot love women as indicated by the indifference to Yvonne].
? Develop Hero and Shape Shifter relationship [Rick and Renault outside the cafe]. Reference the hero's back story.
? Foreshadow of the Call to Adventure and the Refusal [Renault refers to Victor; Rick explicitly states his Outer Challenge - "I stick my neck out for nobody."
? Call to Adventure [Renault explicitly tells Rick not to sell Victor the Letters of Transit; foreshadow of the arrival of Romantic Competitor and Romantic Challenge; on the way to the safe sequence].
? Develop Hero's backstory and capabilities for the Journey [we learnt that Rick fought for the resistance].
? Refusal of the Call [Rick refuses to aid Ugarte; "I don't stick his neck out for anybody"].
? Interdiction [Strasser threatens Rick with his past if he helps Victor].
? First Threshold. Arrival of the Romantic Competitor and Romantic Challenge [Victor and Ilsa].
? Foreboding [Sam distressed at seeing Ilsa].
? Warnings at entering the First Threshold [Ilsa feels they shouldn't stay].
? Romantic Competitor's status [Berger reveals himself and is "at his service."]
? Meeting Allies. Romantic Competitor and Romantic Challenge meet the Shape Shifter. [Victor and Ilsa meet Renault]. Referencing the Hero Wholesale Monta Ellis Jersey , the coming adventure.
? Inner Cave. Confrontation between the Antagonist and Romantic Competitor [Victor and Strasser face off]. A future confrontation between them is established [Strasser demands that Victor comes to his office].
? Fearful of the Journey [Ilsa afraid for Victor].
? Physical Separation [Victor finds out what Berger knows; Ilsa and Sam recognise each other and talk].
? Warnings against the Journey [Renault watches over Victor; Sam asks Ilsa to leave Rick alone].
? Hero and Romantic Challenge backstory referenced [Rick and Ilsa note their past]. Hero affected by the meeting [Rick joins them for a drink and foregoes the bill].
? Foreshadow of the Road of Trials [Renault reminds Victor about the Meeting].
? Hero's Inner Challenge made explicit [Rick can't get over Ilsa; drunk in the bar]. Warnings by Ally to avoid the adventure [Sam tells Rick to forget Ilsa]. References to the back-story between the Hero and Romantic Challenge.
? Hero and Romantic Challenge back-story illustrated (we see them in Paris ).
? Conflict between the Hero and his Romantic Challenge established [Ilsa comes back to talk to Rick].
? Antagonist and Shape Shifter enhance their plans [Renault and Strasser make plans for Victor and Rick].