I was googling something unrelated and the search results included a link to a guide that by all accounts should not be published. This: https://access.redhat.com/documentation/en-us/red_hat_jboss_brms/6.0/html-single/getting_started_guide/#Revision_History

It's the JBoss BRMS 6.0 Getting Started Guide, last updated in 2014. BRMS is not listed on the docs splash page at all since it's been renamed, and the category doesn't seem to exist (clicking "Red Hat JBoss BRMS" in the top navigation menu goes to a 404 page), so users can't access it from the Portal - but at least this book is still up when it shouldn't be, and it's accessible through search engines. I suspect other old BRMS guides are accessible from Google as well. Someone should probably make sure they're unpublished so people don't continue finding them while searching.