What I know is that Costco soft products of the same brand always seem to work better for me than the same thing bought anywhere else (and btw they are rarely the lowest price at Costco). The wife won't let me buy any shampoos or soaps elsewhere. Except Axe of course, as I'm the only one using it so it's ok if I guinea pig myself for science.
Not sure if it could be related to the quantities. Would a 2qt can of shampoo age better than a 1qt one - IDK.
It is also ABSOLUTELY a thing in Europe, between Western Europe and Eastern Europe. We've been vacationing there and say Dove soap bars or shampoo bought locally after we run out of the ones we got with us were day and night worse. Official stuff, official store, etc, etc. A Dove shampoo bought in Germany is leaps and bounds better than a very official one bought say East of Hungary.
Then again, they do that for cars, why not for shampoos and soaps

A Renault you buy in France would be made there, buy it east of say Austria or Hungary, they'll be made in Turkey.
As for drinks on Amazon - they are the same. I used to get Red Bull from there - exactly the same as store bought. BUT, you have to account for storage and delivery. Amazon's could sit somewhere for ages, whereas Costco is controlled chain.
And of course, let's not forget that the Coke that the whole world drinks is the Mexican Coke sold at Costco (made with sugar rather than with high fructose corn syrup), whereas the Coke sold in the US is to outsiders a sugar bomb with no taste whatsoever.
And for anyone who remembers - Mexican Coke (and world coke) tastes like Coke II that bombed in the early 90s.
Pepsi, strangely enough, tastes the same everywhere. And for the record - I MISS Crystal Pepsi. I loved it
And last but not least - some official things on Amazon might not be as official as they claim to be.
My Santa Fe oil filter bought from Amazon (said "
Hyundai store") mentions "
To be used only on Korean market" on the package. Things could be for the Mexican market. Plenty of ways to have official stuff that is official but not US official.