My 2007 return was postmarked 4/18/11

Actual IRS reference that 4/18/11 is legitimately the last day (most are third party):
IRS Has $1.1 Billion for People Who Have Not Filed a 2007 Income Tax Return

I was told by an IRS representative on the phone before I filed 4/18/11 was the last date. I was also told I was good during a conversation where I called to confirm receipt.

I am currently trying to find my certified mail receipt but having a bit of trouble. I was careless with it once I was told by an IRS representative on the phone it was received and I was good!

I know in this case I feel strongly I am in the right. I just need help/insight on how to BEST proceed. Thank you in advance.