If the reprint payslips need to be authenticated (I don't know, because they were technically printed by the company), that can be done in the same employer letter. Just have the employer add a sentence saying something like 'the payslips dated x, y, and z are authentic copies reprinted by Company's HR department at Mr. Lastname's request, and the payslips dated a, b, c, d are original and authentic.'
If the letter contains the word "salary", be very certain that he does, in fact, receive a regular and steady salary, and he's not an hourly wage employee. The income calculation is done differently for salaried vs non-salaried employees, and if he's non-salaried but they use the salaried employee calculation, he could come up short.
He doesn't need all of his historic pay rises to be mentioned, but he will want to list his most recent and any pay rises that occurred in the last six months to help explain his payslips.