I mean there could theoretically be manufacturing differences. If newer techniques replaced older techniques and in the process something was changed, flavor could be changed. A great example of this is pot still whiskey versus column still whiskey. They taste different because the physical properties of the stills are different which will have different degrees of rectification. Hell, the distillers of the 50s could have different palates than modern distillers and take different cuts. Or the yeast was changed which is a huge part of the flavor.

I don’t mind genuine whiskey conneseirs. It’s the speculators who don’t give a shit what it tastes like and just want to make a buck that annoys me.