While watching it, I found a remarkable similarity between the movie and a still alive Great Actress of that time (the play was of 1898), whose name was even mentioned in the movie once, though not in the context, Sarah Bernhardt.
Some natural changes (and a few major ones) were made. Most probably, this being Hollywood Production, even in non-code era, some codes needed to be followed. But that didn't really hide the similarities to great extent.
If We equate Zaza to Sarah, Rigault (the avuncular manager) was almost like Alexandre Dumas, who had been a similar paternal mentor (sans the managership) of Sarah. Florianne could well be Zaire-Nathalie Martel, the senior actress of Comédie-Française, with whom Sarah indulged into physical. Though that was on different context, due to the mistreatment meted by madama Nathalie to Sarah's kid sister, but that too was a cat-fight alright. Here for a change the two made up, where as in real life Sarah and Nathalie didn't.
Bernard Dufresne was obviously Prince Henri Maximilien Joseph Charles Louis Lamoral de Ligne. Here a small 'moral' change had to be done, probably due to censor or censure - the absence of physical relationship, that had in real life culminated into the birth of Sarah's only child, Maurice. The parting was necessitated by 'state affairs' and 'diplomatic act' though a bit different type. Here the child's, of a different gender, mother was Defresne's wife, not Sarah (Zaza).
The Duke, and other lovers, that happened in real life, was naturally not permitted to happen here, the morality clause issue. Of course movies like La Boheme or Camille didn't stop the heroine from becoming mistresses of dukes or Barons. Here too that should have been done, instead of Duke trying to make her a morganatic duchess.
When the Prince comes back much later, in real life as well as in movie versions, to accept the child as his own, despite having shirked from the responsibility earlier. In the later movie version (1939), Zaza rebuffs him, whereas in the real life, the son, Maurice did, telling him in no unclear terms, that he was proud to hold the Bernhardt name, and didn't need another. The variation here could have been audience demand.
The temper of Zaza was remarkably similar to Sarah, who too would throw things at people, at slightest context.
There are many other factors, like rise of Sarah from Starlet to Star, after Prince Episode, or her works during war, trying to cheer up the soldiers, despite being sick and almost immobile (and with one leg amputated). Here of course Zaza is still young, but she was active in war efforts, at least so hinted in the passing comments.
I wonder didn't Sarah herself notice these, she was not only alive but at her prime during this period (1898, theater version, not the movie), or was the theatre better masked to hide similarities ?