I run into a lot a few people who do not enroll in Part A when first eligible due to having employer insurance.
Part A is "free" for most people and pays nothing if your other plan is primary. If you aren't enrolled in A you can't receive your SS benefit. When you do enroll you might be subject to a penalty. Seems like a lot of potential traps to delay something that is "free".
Under the current rule, any retiree who opts out of Part A also forfeits all past and future Social Security retirement benefits. This means that seniors would stop receiving a Social Security check and would be required to repay any benefits received prior to disenrolling from Part A.
COBRA is not creditable.
That's a new one on me. COBRA is the same coverage as your group plan. It is technically a group plan for one but is not the same as an individual plan.
In some cases the group drug plan may not be considered creditable which can trigger a penalty on Part D but never heard of COBRA not being creditable for pre-ex purposes (Medigap).