This verse actually continues the sentence begun in verse 17 and is a subordinate temporal clause beginning with “until the time in which.” In order to make the sentence less difficult for the English reader, the Good News Translation has divided it into two parts (see also Jerusalem Bible, New English Bible, Phillips). Who had not known Joseph is true in a temporal sense, but the primary reference is to the unwillingness of the new king to be guided by what Joseph had done for Egypt.

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on The Acts of the Apostles. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .