I'm not sure what FR's distillation proof is. My guess would be they distill at 130-140 and let it down to 125 for the barrel. From there, the ones that do not increase in alcohol will go perhaps (over 6-7-8 years for the Single Barrel) down to 110 or less and as you suggest are reduced a bit to meet the 100 proof requirement for this brand. The ones at 13 years plus go lower simply because the process is going on that much longer (exterior humidity reduces the water coming out of the barrel while letting the alcohol out untramelled). But say they distill at around 110, well then the drop over 7 years might be to 105 and 100 or so for the older ones. In other words, I don't know the loss rate of ethanol and the distilling-out proof and am just giving examples of what I think happens but the first one is (in my belief) probably closer to the reality.