Here is a partial quote of the review about RR's singing on the CD:
Sparklingly remastered, this soundtrack is big, brassy, and quite enjoyable. It is a good (not great) rendering of the score, made even more expansive by the terrific work of Frank Perkins' adaptation of the score for the Warner Brothers orchestra. At the end of the soundtrack selections are the outtakes of Rosalind Russell's fully orchestrated vocals to "Some People", "Small World", "You'll Never Get Away from Me", "Together", and "Everything's Coming Up Roses". Prepare yourself: she's even worse than you've heard from the rumors. Astonishingly off-key, and even off-rhythm sometimes, it is really mind-boggling to think that this is THE performance of THE role in THE feature film of the property. While these outtakes won't make your viewing of the finished film any less enjoyable, I defy you to ever watch it the same way again!
Thanks to Rhino and Warner Brothers for giving us this package of pleasure and pain.