Yay, we found the payslips!
So I can do the following:
Aug 2017 = HMRC letter for me, payslip for him
Jan 2018 = dual water statement (or HMRC letter for me, DVLA letter for him)
June 2018 = dual water statement
Nov 2018 = dual energy statement
April 2019 = TBD
Sept 2019 = TBD
It shouldn't matter that the August 2017 payslip is from his old company, right? Its a mailed payslip, with the company name on it and his first inital + last name.