There has been one clarification to the text:

  https://github.com/numpy/numpy/pull/11488

For the legacy RandomState, we will *not* be fixing correctness bugs if they doing so would break the stream; this is in contrast with the current policy where we can fix correctness bugs. In the post-NEP world, RandomState's purpose will be to provide across-version-stable numbers for unit tests, so stability is primary. I don't expect to see many more bugs, except in arcane corners of the parameter spaces, like in #11475, which can be avoided, and we can introduce warnings to help users avoid them.

  https://github.com/numpy/numpy/pull/11475

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Robert Kern