In order to receive the Delayed Retirement Credits (DRCs), must the individual keep working beyond his Full Retirement Age (FRA), say, to age 70? Or can stop working at any age (assuming required number of credits are earned), but wait to file for benefits until age 70? The SSA told me that the individual must work past FRA to receive the DRCs, however I have been unable to find that in writing. From an actuarial standpoint, it would seem that if some delayed filing until after FRA, the benefit should increase (DRCs should apply) and the individual would NOT have to work beyond FRA. So is it the continued working past FRA or the delayed filing that determines whether DRCs apply?

Jude,
Earning delayed retirement credits (DRCs) has nothing to do with working. DRCs are earned by delaying receipt of your Social Security retirement benefit past your full retirement age (FRA). Please see Section 720 of the SSA Handbook: https://www.ssa.gov/OP_Home/handbook/handbook.07/handbook-0720.html. So, no, you don't need to work past your FRA to earn DRCs, you just need to delay taking your retirement benefit.
Best,
Mike