The idea drilling the holes for the exhaust bridge I beleive is recommended but not nessecary<sp>It is meant to give a little bit more lubrication and cooling to exhaust bridge. I would ride it since you have the bike back together but the next time you redo the piston and or rings look and see if the piston is scuffed.
I do not know if the differences between the types of pistons make a difference<cast or forged> or that if you have some scuffing that the lack of oil holes are the direct problem.
It is somewhat of a pain to drill those holes. Putting the wrist pin , bearing and piston on the rod , sliding the jug down running a couple of nuts down snug for it, reaching up thru the exaust port with a felt tip pen to the thinnest part of the bridge, slowly turning the engine over marking the piston. Take it all apart again, finding the middle of the two lines you just made, finding the heighth on that center line where you are supposed to drill.
keeping thedrill bit from walking since it is something round you are trying to put a hole thru. I am leary on smacking my psiton with a center punch<call me chicken but thank goodness that it is aluminum and the drill bit shoud bite right in> . Deburring the holes you just drilled, and then recleaning everything
It is a smidgen easier then the way i tried to explain it but if I HAD to do this everytme I installed a piston I would probably buy the stock piston only because the factory didnt think I needed it and I dont have to do it. The majority of my decision resting on the idea of if the piston manufacture says I need it then they should do it when making it. I know that a a particular piston wil usually fit a few different years of a model , some with exhaust bridges some without . But my idea is I am spending My money Your product better fit my needs and nothing more.