Zador was, indeed, the orchestrator of ALL of Rozsa's films from THAT HAMILTON WOMAN (1941) to THE V.I.P.S (1963) (and virtually no others during that same period, if you can believe IMDB).They obviously had a very good working relationship, since Rozsa brought him along when he signed his contract with M-G-M in 1948. Said contract specified that Rozsa could pick his own orchestrator (the contract said "arranger") even if it meant the studio had to pay more than minimum scale, and I suspect that clause was there specifically so he could get Zador's services.

To answer your original question, Daniel, the two Rozsa "short" scores (looking more-or-less like piano music on 2-6 staves) which I have seen and studied in depth (CID and HOOVER) are sufficiently detailed that, as Shu so perceptively put it, Zador had merely the "task" of fleshing out Rozsa's "sketches" into full orchestral scores and then creating individual orchestral parts (although others at the studio might have done that). I am sure that absolutely no "compositional liberties" were ever taken or even allowed.

"Orchestration" means so many things, and is so misunderstood in Hollywood lore. There is a world of difference, for example, between the Rozsa-Zador team where Zador provided a service that any appropriately-trained college music major could do, and (for one example) the Chaplin-Raksin team, where Raksin took Chaplin's (whistled?) melodies and turned them into full musical compositions. Another extreme example is the Bob Merrill-Leigh Harline score for THE WONDERFUL WORLD OF THE BROTHERS GRIMM, where Merrill created tunes on a toy xylophone(!) which were written down by an assistant and then fleshed-out by Harline with form, harmonic substance and orchestral color. Compare those cases with Bernard Herrmann, who was outspoken (Herrmann??) in his insistence that only he himself would ever write out his full scores.

And all of this is different from "orchestration" in the sense of taking a work for another medium (usually keyboard) and transcribing it for orchestra (Mussorgsky-Ravel's "Pictures At an Exhibition" or Stokowski's Bach, to cite two very famous examples). (Marching band transcriptions fit in this category too! )

And in today's world of computers, synthesizers and digital "mock-ups" I suspect it means something else yet again!

But never fear - any Zador-orchestrated score you hear is 100% Rozsa!!