Benefits that are lost due to the earnings test, when are they recovered? Is it in the years when there are no longer earnings, at FRA or some other time? If one wants to track this to make sure they are fully recovered, how would one go about this?

Also, do the same rules apply to widow benefits lost to the earnings test?

Deb,
The Earnings Test is only applied if you took benefits before your full retirement age (FRA) and have earnings above the exempt amount. Since Social Security is intended to provide income in retirement, the Earnings Test is used to determine whether you've fully retired, if not your benefits are reduced. The benefits that are lost due to the Earnings Test are not recovered. Rather, the early retirement reduction factor is adjusted at your FRA to account for early benefits that you didn't actually receive. For an extreme example, suppose you took your benefit four years early, which means that it was reduced by 25%, but, due to the Earnings Test, you never received any early benefits, then at your FRA the early retirement reduction factor would be eliminated and your future benefits would not be reduced. It would be just as if you didn't take your benefit early.
Yes, the same rules apply to widow's benefits.

Best,
Mike