I wouldn't call it drastic, but there was definitely a change. My theory is that Florence wasn't a natural soprano anyway. She could certainly sing it- and sing it well- but her natural voice was not that high. It's possible that there may have been some damage or wear and tear on her voice that became noticeable in 1967. Diana underwent a similar period a year or two later where her voice is noticeably raspy. I imagine Diana was given proper attention to this, while Florence unfortunately was not.
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