I didn't mean "checks" literally, just a deposit into my checking account where our regular SS payments also go. I did continue to work past the full retirement age, which for me was 66, and started drawing SS at that time even though I was still working. I calculated how much I would be foregoing if I waited until age 70 to apply, then calculated how long I would have to live beyond 70 to make up for not drawing it for those four years. Turns out I would have to live to at least 87 to break even, so I decided to get the payments as soon as I was eligible rather than gambling that I would live long enough to gain by waiting until 70 to get the higher monthly amount. When I look at the additional funds they sent me, that started this thread, and calculate back to Jan 2014, the difference comes to about $33/month extra for both my wife and myself, total. So likely it was just sort of adjustment.
By the way, for those of you who work past 65, be aware that even if you are working you become eligible for Medicare benefits as soon as the month you turn 65. The Part A benefits cost you nothing directly (covers hospital care) but you have to pay for the Part B benefits (covers outpatient care up to 80% of the allowable charge). The amount you pay for Part B can vary considerably depending on how much you are totaling earning, so if you keep working you will pay a lot more for this Part B benefit than will the person who stops working at 65 and whose income is limited to SS and whatever pension, if any, that they are getting. I was paying more than double the basic Medicare Part B charge for several years, but once I retired at age 70, the monthly fees for Part B went down the following calendar year.