"Sir Robert Sheffield was born 1166 (12 Henry II.), ..."
The pedigree appears to be copied from The Peerage of England, as published in 1735, which doesn't give a birth year for Sir Robert. No source is provided for the birth year, which is stated as being "in the year 1166 (12 Henry II.) one hundred years after the Conquest". One wonders if the thought first occurred that he was born about 100 years after the Norman invasion and then the year transformed from speculation to "fact". 1166 seems a little early to have had a great-great grandson who fought in 1356, assuming that the first 3 generations were through the eldest son.