My I interject an interesting story here about thinning the proof?
Springbank 12 100 Proof (Circa 1990s) per LAWS web site.
This is the now-legendary "12/100," often referred to as "Double-Dark / Dark-Dark" or "Single-Dark / Dark" depending on the color of the whisky (there seem to have been 2 different batches/vattings).
As the story goes, in the mid-1990s it turned out that Springbank had a number of under-proof casks aging in their warehouses, between 30 and 36 years old. Since the spirit needs to be at least 40% ABV to qualify as scotch whisky, somebody at the distillery decided to use the under-proof whisky to "dilute" cask-strength around-12-year stuff down to standard levels. Typically, distilled water would be used for this purpose -- so you can imagine how instead adding 36-year-old unadulterated Springbank might impact the flavor differently than water! Another version of the story says that there was a family dispute at the time, and one of the guys at the distillery "wasted" these great casks to spite someone else.
According to the guys of PLOWED who shot this bottle into fame, there is little difference between the "darks." Some disagree though.