Advisory conflict resolution affects mirror sync case
Currently advisory conflict resolution assumes that advisories from a base/previous version are always present in the new one. It might not always be the case (e.g. mirror case). Current behaviour leads to wrong results - either more advisories are present than needed, or the error is raised due to inability to resolve advisory conflicts.
resolve_advisories should check whether any conflicts are present in the current version and only then, look into previous version for such advisories to figure out which ones were present before and which ones are being added.