Signing NHSC job contracts early

I have been told since I was a medical student by scholars to "look for sites early". I started that process and some sites seem interested in offering contracts early as well, since they can only have one scholar per site. However, the people I have talked to at the NHSC say it is not possible to sign a contract early because we don't know the HPSA scores until the year of and if a site will qualify for a given scholar.

Did any of you sign before your last year of residency? If so, did you...

Signing NHSC job contracts early