Pagure (at least the pagure.io instance) does not allow git fetch unadvertised commits. When trying to do so this happens:

$ git fetch origin 484327c7ae43d5ea6cae03f826012f996ef1d2b7
error: Server does not allow request for unadvertised object 484327c7ae43d5ea6cae03f826012f996ef1d2b7

It is easy to try with whatever commit not referenced or being in a history of any branch or tag. Note you have to use full hash of the commit (rather to say, an object hash).

This would be beneficial e.g. when trying to find differences between force-pushed rebases of PRs locally on a client machine, where history has not been fetched in time and hence lost from local git copy point of view.

One might argue this is a security measure, however these are already available via Pagure's WebUI as links in a PR's web page, so not much would actually change security-wise.