I gotta go with Judy on this one. While it will be a major pain to do this it is the only proper way and do hope the folks at the IRS who are processing the amended or correct 941's (used to be form 941C) that they can add and understand your explanations. BTW, do as an IRS agent advised me, keep your explanations simple so a 10th grader can read them. Took me three years to convince the IRS one of my clients had over paid his payroll tax for the first quarter of the tax year and the overpayment was applied to the second quarter of the same tax year (correct way to do this according to the IRS regs at the time) which started the snowball rapidly moving down hill. Office audits, penalties, penalty abatements and even visits from IRS agents and all a bunch of crap but finally settled when someone inside the IRS took the time to go Oh, I see what happened here. Good luck and charge accordingly.