Github user StefanRRichter commented on the issue:
https://github.com/apache/flink/pull/5490
The docs are not "incorrect" and this is on purpose. Background is that, in
general, externalized checkpoints are only required to support a subset of the
features that savepoints provide and we do not want that user rely on their
checkpoints to be rescalable. While this might be true now, this might change
for all or some implementations in the future, so we simply do not want to give
a guarantee that we then must maintain.
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