I just received an MBA update (effective Oct 1) and lump sum for DRCs. October? Whatever.
But, I believe the lump sum is short. Specifically, it looks like SSA gave me 9 months DRC credit
(correct), but lump sum was 9 months worth, matching checks received for 2018. However,
I started SS Nov 1, 2017, so I believe SSA still owes me "backpay" for those 2 months in 2017.
My question: does SSA do DRC catch up in a single go, or is another check in the mail?
I can't say for sure without more specific information about your case, but it doesn't sound like you're due any additional back pay. When you file for Social Security retirement benefits between your full retirement age (FRA) and age 70, your initial benefit rate only includes credit for the delayed retirement credits (DRC) earned through December of the year prior to your month of entitlement.
Therefore, assuming that you're saying you reached FRA in February 2017 and filed for your retirement benefits effective with November 2017, you would not be eligible for any credit for DRCs for the months November and December 2017. The 9 months of DRCs you earned in 2017 would not be creditable until your payment for January 2018 (https://secure.ssa.gov/apps10/poms.nsf/lnx/0300615690).