I bought a Maxxis tire at Discount tire on order. When it came in it was about a year old by the date code on the tire. I voiced my concern and was told that the warranty starts on the date of the receipt not the tire. I contacted their home office and they confirmed it.
The reason this was important to me was that Maxxis has a 6 yr manufacturer defect warranty and previously I had to make a claim on the 5th year for tread seperation and contacted Maxxis and they told me it went by the date code on the tire, but later admitted that they honor the receipt date if I still had the receipt . I got a new tire for about $35 under warranty !
So keep your receipts. I now shoot a picture of all my receipts with my phone and transfer a copy to my computer because most receipts are unreadable within a couple of years.