Change Impact and Upgrade Guide - On Premise Release 14.1.00 says
If any patch level is installed on the base version 13.1.0
(that is, 13.1.0.1 - 13.1.0.5)
Installation of 13.1.0.9 is recommended before the upgrade to Release 14.1.
If you want a second opinion open a case with support.
Not being a techie and not understanding the minor technical finesses of versions that sounds to me that the development of 14.1 release and the documentation departed from v.13.1 at some point and patch 13.1.0.9 brings v13.1 back to being compatible for upgrade.
You can always test that, as the instructions always say that you do the upgrade in a test environment (and be ready to roll back if it goes to dogs - looking a the threads that is known to have happened.).