In 2025, AMD made changes to their microcode signature verification following
publication of CVE-2024-36347.

https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7033.html

As a result it is not possible to install the latest microcode release on
systems which have not had their platform image (usually included with BIOS)
updated.

This directory contains older versions of microcode for affected systems,
which is used as a fallback when the latest microcode is not accepted by
the CPU.