I became a US resident (Green Card holder) in the summer of 2012, so the first tax return ever filed with the IRS was a dual status return for 2012.
I used to have a job in my country, that I quit before becoming a resident (in mid-April 2012), so when I filed that 2012 return, I never stated income from that foreign job because it was not connected to the USA in any way and it fell under the non-resident part of 2012 US tax return.
However, the foreign company I used to worked for had a yearly productivity bonus scheme in place, that was payed to employees in the year after it was accrued (since it was based on a some year-long analysis of employee's productivity). So in June 2013 they issued me a year 2012 bonus payment of around $750 (gross; I actually received the net since much like in the USA, employment-based income is subject to tax withholding by my country).
Then when I did my 2013 US taxes (this time as a regular full-year US resident) in winter 2014, I completely forgot about including that sum in my income.
I've applyed to become a US citizen, and I would like to have my US tax status fully compliant with law in case they ask me to prove that I did not receive income from outside the USA while being a US resident.
My question is: do I actually really need to state that $750 income in my US tax return, given that even if payed to me in 2013, it's effectively connected to the job in my country in the non US-resident portion of 2012?
If I indeed need to amend my return, can some confirm that I need to amend the 2013 one?
If I need to amend, can I use form 1116 to ask a credit for the 10% foreign taxes withheld?