Remember too that nock tightness is relative to the weight of the arrow as well as the poundage of the bow.
I shoot heavy bows and heavy arrows so if I compare my nock to the nock tightness of a lighter bow/arrow setup, it may seem a little more but it is not taking the percentage into consideration.
As already mentioned, the serving wears a little and the nocks themselves seem to loosen up a bit with time too.
I don't like hunting with nocks that are too loose, so as others have said, take it slow and easy when adjusting the nocks.