We have the opportunity to classify the photos between 0 stars and 5 stars, but if you have 0 stars on a photo, you can know if this photo is classified or not. What about adding a new option in the classification option as no classified yet instead of 0 stars?
I have always wanted this distinction for the pick flags - i.e. to distinguish:
* Hasn't even been consider yet, from
* Been considered but still undecided (unflagged).
The distinction for rating makes sense too.
You got my vote :-).
In the mean time, consider a work-around:
* When rating has been considered (and the answer is zero), mark a photo with some corresponding metadata value (e.g. custom metadata or an unused IPTC field). Until such markage, unrated/0-star photos can be considered "not yet classified".