Enhanced typesetting is complicated. It requires the book to be sent to your device in KFX format. That can fail to happen for several reasons. You might have bought and downloaded the book before it was available in KFX.
Another reason for failure is that KFX keeps having new features added over time and the books and reading software are updated frequently. If you do not have the latest firmware on your kindle you may not get some books delivered in KFX.
And as was mentioned you are usually locked in to the version of the book that was current at the time you bought it. Even if the book is subsequently updated in most cases that will not be made available. But in that case all of your devices me will receive the same version.
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