Hi,
I am filing my 2009 taxes late. My income was below the exemption threshold and
I thought I did not have to file taxes(I was wrong).

After filing for 2012 taxes, I realized my mistake and now wanted to file 2009 forms. What I was wondering is what should I write in "c) Number of months claimed in prior tax years" in the Tax Treaty Income exemption heading?
I claimed 12 months in 2012 but I am not sure how 2012 can be considered prior tax year for 2009 tax form)

What should I do?Should I write 12 (0 would be fraudulent-wont it?) to take 2012 taxes into account or should I write 0(since before 2009 I didn't claim anything)

Put the number of months you were in country prior to the tax year in question, whether you filed or not.