We specifically add Release Notes for all known customer issues that are specifically resolved by the release / patch. As the standard response for issues where the customer is using an EOSL / unsupported SDK version is to request a reproducible test case using that latest version, being asked to test with such a version does not automatically mean that support know that the issue is resolved by the release in question.
In this case, the issue may have been addressed internally within Engineering. If this was not done in respsonse to a known customer issue then it would not have been added to the Release Notes. It may even have been "fixed" as a side effect of some other change.
It is impractical to add release notes for every known defect found within Engineering / QA testing of a product. This is standard practice within the industry.