As birth or baptism dates have been lost, all of their birth dates have been approximated from other archival evidence such as death dates of other family members. Similar to the archival evidence surrounding Frans Hals, the first known commissions for Jacob Cornelisz were from when he was at least 35 years of age. It is assumed that he worked in a painters's workshop before that, and judging from his close copies of Haarlem painting techniques, this was possibly in Haarlem.