git modules used by qemu are usually tracking the master branch, so a shortlog works fine and shows the additional comments. But when it's switching branches, the shortlog doesn't provide the diff between the branches, that is the commits that were not already in the branch being tracked. In my last update (https://patchew.org/QEMU/20210125073427.3970606-1-marcandre.lureau@redhat.com/20210125073427.3970606-2-marcandre.lureau@redhat.com/), I used a tool called git-cherry-diff, but there might be git log arguments to do that I ignore.