I am not an expert but we all know that metal, or any other substance, expand and contracts with heat (water being an exception). I looked up temperature and pressure relationships and got a formula based on Gay-Lussac's Law. I plugged in the numbers assuming that the ball was inflated with 100F air at 12.5 psi then I changed the temperature in the formula to 60F and the pressure computed to 11.24 psi. A 40F temperature drop caused a 1.25 psi drop. This explains why your automobile tires seem low in the winter. Nothing in the rules states what temperature the inflation air should be, only that the balls should be between 12.5 - 13.5 psi at the official check time. How coincidental is it that 11 out of 12 balls deflated the same amount....I like to watch the patriots play even though I am a Giants fan. I would be devastated if the NFL was marred with fraud (which its not).