There are 2 parts to the Lifetime warranty that come with these switches.
For the first 90 days (3 months) you have access to 24x7 Tech Support, once that timeframe expires it reverts back to Business Hours Tech Support.
My guess would be that the switch was purchased by the reseller in December. If they don't buy direct, then it is possible that the warranty period was activated from when they bought it from their distributor (which is not really how it is supposed to work).
Add the device to your Aruba Support Portal login and you will be fine.