I responded to a CP2000 for tax year 2016 with the CP2000 response form disagreeing with the assessment on the CP2000 (they used the proceeds of a 1099-B stock sale as income without the cost basis), 1040X amended return, a copy of the missed 1099-B and 1099-G from state taxes that I had missed as well, a letter explaining the issue and a check with just the tax amount owed. The problem is I forgot to write CP2000 on the top of 1040X as per the instructions. Should I contact the IRS to let them know? Will they send me a bill for the interest and penalties afterward?
