Milk

I bought a bottle of milk the other day and as usual I checked the expiration date. What bothers me the most and I cannot seem to understand is why are there two expiration dates? If you live in New York or neighboring cities, have you noticed this as well? NYC gets an earlier expiration date. And I want to know why!

Do New Yorkers have a more delicate stomach and therefore cannot handle milk that is a few days older? Does it spoil faster in New York than in New Jersey? It’s on all my milk and not just the Cholov Yisroel ones. I don’t understand this dating system and would really like to get to know the ins and outs of this phenomenon. Does anyone have any suggestions?

I can understand expiration dates on items like milk and bread. But why are there expiration dates on bottled water? Does bottled water really go bad? Is it really going to turn sour if you use past the expiration date? Is it going to spoil? Does water really spoil?

Another thing while I am at it, does medicine expire? Why do we have expiration dates on everything? Is it possible to pick something up that won’t perish? Is there?

My peeve is still on the milk. It still annoys me after all this. Where can I find how the expiration dates work? Is there a way a mathematical equation? Or they just know when milk is going to turn bad and date it for that day to be the last day?