I just bought my second pair of running shoes from my local store. The store owner and only salesman is (or claims to be) an expert in biomechanics as it pertains to walking and running, and I have no doubt in his ability to identify the right pair of shoes for my needs. People are allegedly also traveling from all over the country to get advice from him.
However, today he made the claim that the variance within shoes even within the same model and year is large enough that you can't know that a certain shoe is right for me without doing a proper video gait analysis with that specific pair. Of course, he has financial incentives to ensure that I buy my shoes from him instead of stocking up on the same pair online for half the price.
Is this a bogus claim from his side, or do you find that the variance between pairs of the same exact model is non-negligible?
FWIW, he's identified that I pronate more on the right side than left, and that my hip is a bit stiff on the left leading to increased risk of injuries due the lack of flexibility. In both cases he has ended up with stability shoes for me.
Unless it's a bargain basement brand and quality control is absolutely horrible I'd be shocked if there was much variation at all within the exact same model of shoe. If a particular style and year model of shoe works for you, any off the rack version of that shoe (barring major defects) is going to work for you.
If nothing else I'd expect whatever miniscule material differences there might be are going to get completely overriden by differences in wear from your specific running and terrain pretty quickly.