RSA-5 Duplex - Use Registration Permit

[Amanda Sterling]

I'm looking at a property that is zoned RSA-5 and is set up as a duplex (with separate gas and water meters). It does not currently have anything on file with L&I for a certificate of continuing use as a duplex. The seller has owned this property since 1970. I've called a few attorneys and am waiting to hear back, but has anyone had success (or failure) in a situation like this? 

Thanks so much!