The purpose of leaving those two positions unpunched is to offset the weight of a valve stem so the rim will be reasonably balanced to start with before adding a tire. Some mfgs leave the yellow dot (lightest point) off the sidewall if their process produces a tire that they decide is close enough.
High spot / radial runout is often marked on newer oem rims and easily checked on older ones. This aligns with a red dot on some tires that identifies the flatter/thinner/ lower radial runout of a tire so the assembly has less runout and is more important than yellow dot placement.
Storage conditions of the unmounted tires can cause them to appear out of round when spinning on the balancer when first mounted to the rim because they are cold and may not have been stored on a tire rack, so not a good time to try to check for out of round in the mounted tire for balancing. If there is a red dot, use that. The rack spreads the tire weight across two bars about 90 degrees apart versus on the floor leaving a flat spot or on the side that may or may not be any better and likely stacked.
High spot / radial runout is often marked on newer oem rims and easily checked on older ones. This aligns with a red dot on some tires that identifies the flatter/thinner/ lower radial runout of a tire so the assembly has less runout and is more important than yellow dot placement.
Storage conditions of the unmounted tires can cause them to appear out of round when spinning on the balancer when first mounted to the rim because they are cold and may not have been stored on a tire rack, so not a good time to try to check for out of round in the mounted tire for balancing. If there is a red dot, use that. The rack spreads the tire weight across two bars about 90 degrees apart versus on the floor leaving a flat spot or on the side that may or may not be any better and likely stacked.
