I got my Green Card (GC) in 1990. But could not settle permanently in the USA until 1996. I kept my GC alive by returning to the USA once a year for short trips.
I did not file any tax returns until 1997. I had no income in the USA and continued with my employment in my "home" country, where taxes were deducted at source.
I checked both with IRS and an attorney if I needed to file for those years (1990-1996) even though, most certainly, I did not owe any taxes. IRS said that as long as I did not earn more that what my salary was, there would be no tax but I had to apply for exemption.
IRS advised that I should submit the returns. IRS mailed me tax forms for 1990 and 1991. The rest are available for download from the IRS website.
The attorney advised that there was no need to file but that I should write a letter along with the N-400 application explaining the situation.
The reason for submitting the tax returns for those years despite having been resident and having filed the taxes for the last five years is that the Naturalization Guide states that we must send this evidence if we were out of the USA for more than 6 months since getting a GC.
I thought it best to file and state on N-400 that I <b>have not failed to file the required returns.</b>