The 'natural pressure change' argument is easy to explore. The formula is simple:
P1/T1 = P2/T2.
Lets take the very outer temperature limits of plausibility, say it was 75d F when they filled them, and 33dF when they tested (you have to change F to Kelvin to work this formula).
12.5PSI / 297K = X / 274K
Solve for X = 11.5 PSI
So even if the temp dropped farther than we know it dropped, at most you would lose 1 pound per square inch of pressure.
In order to lose 2PSI, the temperature the balls were filled at would have had to have been 127d F.
Apparently not that easy as we are now 1400+ posts in and people are still calculating this wrong. The equation is P1/T1 = P2/T2 rearrange the equation to solve for T2 so we get T2 = P2/P1*T1. All units of measure MUST be measured in absolute . For pressure you need to add the atmospheric pressure (14.7 psi) to the pressure inside the ball. The temps need to be in absolute also so either in Kelvin (C + 273) or Rankine (F + 459).
So your example to find a 2 psi drop works out to:
P1 = 12.5 + 14.7 = 27.2
P2 = 10.5 + 14.7 = 25.2
T1 = 75 + 459 = 534
T2 = (25.2/27.2) * 534 = 494 degrees rankine subtract 459 to convert back to F = 35
So the change in temperature is 75 - 35 = 40 degrees for a 2 psi drop in pressure in the ball.
Its not just posters getting this wrong its actual people in the media putting out this foolishness. Felger and Mazz on 98.5 were talking about an 87 degree temperature swing required to get the 2 psi change in the ball.