Questions regarding ARV & appraisal

[Dalton Dillon]

I'm looking to purchase a duplex using the BRRR method. I'm concerned about the ARV due to there not being any comps in the area. Even as far out as 1 year. My question is - How will an appraiser appraise the property without there being any duplex/triplex's sold within the last year? My agent even went as far as going over to the next city/town which is pretty far out and still nothing. Will the appraiser use singe family comps since a duplex is still residential?