The differences you offer in your initial question are rather small, 20 grains in weight and 10 grains in spine. I know that most folks aren't good enough to detect that difference, myself included, and I'm a pretty good shot, or at least used to be, and have been at this more than 45 years.
I won't argue that there is one spine/weight combination that is optimal for a given bow, but what many overlook is that most bows will shoot a fairly large range of spines and weights quite well.
Most of the bows I shoot will handle 20# plus difference in spine with little trouble. I.e., my 55# bows will shoot my woodies of 55-75# equally well. And most of them are not cut to center. I also shoot arrows of different weights, but most are within 20 grains. A 50 grain difference becomes noticeable beyond 20 yards, but again, most couldn't tell the difference on shots closer than that unless they were shooting very light bows.
An arrow that is truly mismatched in terms of weight, spine, straightness, etc. is fairly easy to detect, however.