From memory, the HG612 can handle error counts up to a value of 2,147,483,648 before being reset to zero (2 ^ 31).
(It might even be 4,294,967,296, i.e. 2 ^ 32)
FEC/RSCorr are one & the same thing, but one of them is reset to zero following a Retrain Reason 2 resync (I can't recall which one) & they are both reset to zero following a Retrain Reason 0 resync.
I have no idea waht happens for other Retrain reasons as I only ever see reasons 0 & 2 on my own connection.
the delta value (change each minute) should still be the same for both though.