Here is the response I received from the Embassy. I do not believe that it is as automatic as we may have believed.
We are writing in response to your February 14 inquiry regarding the visa case of Ms.
We note your concern regarding the validity of the K1 petition.
An approved K1 nonimmigrant visa petition (I-129F) is only valid for four months from the date of its approval, however, consular officers may revalidate the petition during the applicant s visa interview if eligibility requirements are met. Each revalidation is good for an additional four months. However, if the officer determines that there is insufficient evidence of continued intent to marry, including instances where no action has been taken on the application in a timely manner (i.e., a visa interview for the applicant and submission of required documentation), the petition may be returned to the approving U.S. Citizenship and Immigration Services (USCIS) office.
We advise the petitioner or the applicant to remain in contact with the Embassy on the steps they are taking to proceed with the visa application.
We hope this information is helpful.
Sincerely,
CONSULAR COMMUNICATIONS GROUP
Consular Section | U.S. Embassy in the Philippines