I believe this is a recommendation, versus a policy.
I wanted to get people's thoughts on it, and if ya'll like it, put it in the documentation.
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In Red Hat Enterprise Linux (RHEL) 8, Red Hat decided to not ship all packages that are built from RHEL spec files.  This will also be true of RHEL 9, and possibly future RHEL releases.  These missing packages are usually -devel packages and may impact an EPEL package build.
If your EPEL package is impacted by a missing -devel package, do the following.

1 - Request the package be added to RHEL 8 and 9 CRB repository. 
-- To initiate this process, please file a bug in https://bugzilla.redhat.com and request it be added to RHEL 8 and 9. Report the bug against the "CentOS Stream" version of the "Red Hat Enterprise Linux 8" and/or "Red Hat Enterprise Linux 9" product.
-- Be sure to say that it is impacting an EPEL build, and which package it is impacting.

2 - Create an epel package that only has the missing packages.
-- Be prepared to maintain this package as long as it is needed.
-- It is recommended that you name it <package>-epel
-- It is recommended that you add the epel-packaging-sig group as a co-maintainer
-- It qualifies for an exception to the review process[1] so you can request the repo with
--- fedpkg request-repo --exception <package>-epel
-- If you need help building this, ask for help.  We have some examples.

3 - When/If the missing package(s) are added to RHEL CRB, retire your -epel package.

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Sorry, this is a little rushed.  I wanted to get something out sooner, rather than later.

Troy

[1] - https://docs.fedoraproject.org/en-US/packaging-guidelines/ReviewGuidelines/#_package_review_process  - Third bullet point