It is quite possible for two identical objects to be generated in one group.
Added 11 minutes later
The value of a regular artifact-treasure is 2000. A quest item can also have a value of 2000, so it is unlikely that you can determine it by its value.
(but each seer has a frequency of 10, while a random artifact of each level has a frequency of 150, so in the case of weak protection, it is more likely that it is just an artifact).