Social Security Deferral

I was reading your column in the newspaper and had a question about what was said about social security deferral:
“Deferring a starting date until age 70 (and specifying in writing that you do not want to take benefits even a day before you reach your 70th birthday) can provide an increase of 8 percent in your monthly check for every year you defer between full retirement age and 70”.
I am currently almost age 67 and have not yet claimed a benefit. My plan is to wait until 70 as you suggest. However, I did not know anything about having to specify this in writing. Why is this necessary, and how do I go about specifying my intent in writing?

Terry Says: If you go to your Social Security office to sign up for benefits slightly before your 70th birthday, which you should, there have been reports of errors in processing.  On occasion the request has been processed to start benefits immediately, costing you a year of that delayed benefit and the higher benefit level.    You want to make sure that the benefits do not start before your 70th birthday.  It’s easier to confirm that in writing that when you sign up in person at a Social Security office.  If you apply on the SocialSecurity.gov website, as most people do now, there is little chance of this error happening, as you yourself input the start date.