The birth certificate thing is important, but it is not that important as lopchand dai says. Source: two of my pals were in the same boat as you and didn't submit that invented "Ward ko chitthi".They attached copies of academic certificates along with copies of passport and citizenship (nepali and translated versions of c/ship) to attest their birthday claims and got their GCs. On a side note, if you were filing I-485 under a different scenario, say H1, then the fireworks start for real. Hope that helps. Good luck!