Confusion regarding number of required payslips

Hello all

My partner (American citizen, living in UK) and I (British Citizen) are currently in the process of applying for an unmarried partner visa. Individually we earn slightly under the £29000 income threshold so we are combining our incomes. Both of us have worked in our respective jobs for over 12 months and have received pay rises in that time.

My question is how many payslips and corresponding bank statements are we required to provide as evidence of our income? The form mentions 12 months, but everywhere online (and some previous posts here) state that 6 months worth is sufficient for people in our situation. I would go with the safe option but my employer is being difficult about providing payslips older than 10 months as they changed payroll provider then and claim not to have retained any copies from before that period. Do I need to escalate the situation and try and acquire those last two payslips or would it be unnecessary?

Thank you!