Major problem (though I love the film)
The "Beautiful Girls" sequence, especially what we see before it settles into the song, is not the kind of musical they were filming then, even BEFORE Don and Lena begin working on their "talkie". We see a boom above the singer, which they didn't think of when dealing with Lena's "where's-the-mike" problem. To say nothing of the generic style, where we see Busby Berleley-esque mise-en-scene.
The film is wonderful entertainment, almost unflawed. But it shouldn't be used by film teachers dealing with the early sound era, unless they strongly qualify much of what is presented (such as, with another example, the immediate closing down of the studios, not recognizing that the process was more gradual.
What can be asserted without evidence can also be dismissed without evidence.