Old Zoning Permits from the 40s for a duplex still valid?

[Forrest Hayashi]

Hi BP'ers,

Currently in the process of submitting an offer on a Philadelphia Duplex zoned RSA5 A.K.A Single Fam. The owner lives in one of the unit and I guess his/her relative lives on the other unit. They didn't have a rental license but I was able to find an ancient zoning permit for 2 family back in the 40s on Atlas Portal. If the deal goes through, would I still need to attain a new variance? and also the dreaded Certificate of Occupancy?

Anyone have similar experience before?

Thanks! :)