There could be several reason why the upstream version of the recipe is unknown (broken link, time out, etc.). The enhancement request here is to include the unknown reason so it will be easier to maintain the broken links or errors that require manual intervention.
FWIW, I think with a) addition of support for repos without version tags in checkpkg b) addition of RECIPE_VERSION_UNKNOWN acknowledgment in recipes this issue is obsolete. When a recipe goes from known to unknown, it's usually because upstream went offline or removed the tarball, and this requires manual investigation and fixing anyway.
See the comment above.