The above cited article and references are most useful, but the subject of THE THIRD MAN has often been discussed at Wellesnet in a lively, thorough (exhaustive?) and sometimes contentious manner (as have most of the subjects we re-hash here, these days). I would suggest to anyone interested, also look at the following thread: viewtopic.php?f=1&t=1060&hilit=the+third+man
I would only add that none of the above materials point to a number of odd touches in THE THIRD MAN, which seem to refer back and forward to Welles' projects.
For instance, I'm sure that I'm not the only one who has noted that Holly Martins (Joseph Cotten) is cast by British Intelligence for cover purposes as a critic (albeit not a dramatic critic, which Cotten had been early in his career), and that he finds himself covering his boredom in attending an 18th Century Viennese farce in a language he doesn't understand (similar to Jed Leland's experience in CITIZEN KANE). The scenes in the play (written for the film) reveal that Anna Schmidt (Alida Valli, a Croatian actress well known in Italian films ), Harry Lime's friend whom Martins has come to see (at the suggestion of "Baron Kurtz"), is not a very good or important actress, more stage decorative strudel than anything else. Then, after Harry Lime's famous cuckoo speech, Holly Martins is bitten on the finger by a white cockatoo, similar to the one who announces the climax of CITIZEN KANE. Whether these are inside jokes or the influence of Welles (now denied all around) is hard to say.
The cuckoo clock reference, btw, is quoted pictorially by Welles after a fashion in the dramatic climax of MR. ARKADIN, made seven years later.
It's always interesting and nostalgic for me to look at these things again.