In checkExternalRepo kojira attempts to cache the overall timestamp of external repos. For a key, it uses the non-expanded repo url (e.g. with "$arch" still present). However, the actual times we read are from the actual repomd.xml file(s).

If a tag has the external repo added to it and has a limited or empty arch list, then checkExternalRepo will only check those arches. The cached value will not factor in any missing arches (which could be newer and used in other tags). If the arch list is empty, the cached value will be 0.

A later tag may have the same external repo with a larger (or any) arch list that would give a different timestamp, but the code will simply see the cached value and not check further.

I suggest we cache on the fully expanded repomd url instead.