I've seen models that have very little traffic and look brand new. I seen some models that are grand central station where C2 would be an exaggeration. It seems reasonable to me that maybe that's why we inspect...to determine the state of condition.
Certainly UAD language allows it. Fannie UAD even address the issue of OP where it is close to both in Question #14
https://www.efanniemae.com/sf/lqi/umdp/pdf/uadfaqs.pdf
which states: "
The Condition and Quality rating that most closely fits the property must be selected. Comments and any additional pertinent information that will provide greater clarity around the choice of the condition and quality ratings must be provided".
The qualifications for C1 are: House must be vacant (goes with page 1 vacant box) and must be "recently constructed" in which an extended time vacant falls within the meaning of "recently constructed", but must not have
Significant Physical Depreciation due to lack of upkeep.
If the appraiser's inspection shows support for a C1, then he's not wrong.
If the appraiser's inspection shows support for a C2, then he's not wrong.
If the appraiser's inspection shows support for a C3, then he's not wrong.
If the appraiser's inspection shows support for a C4, then he's not wrong.
If the appraiser's inspection shows support for a C5, then he's not wrong.
If the appraiser's inspection shows support for a C6, then he's not wrong.