Yeah, I use a jewelers scale and weigh every egg as it goes in the bator. In future, I am going to weigh every egg at hatch too. Perhaps the 21 day old eggs have lost weigh more than they should before ever going into the bator...that could explain the common believe that such old eggs aren't viable.
RR = Red Ring, or chick that died in the egg prior to developing. Early in the hatch if your egg, when candled, shows a distinct line around the embryonic area, its a blood ring, and it indicates the egg failed.
Thanks - never saw those initials used for blood ring before. Last hatch I had quite a few, probably due to shipping damage.