The cheek of them!
Spirit off the still is around 68% or so, once the whole middle cut is collected. As noted, the standard practice these days is to cut to 63.5% for cask filling. I've speculated that this is to provide an industry standard so that the excise on casks swapped around for blending will be easier to figure, but that's really a guess out of the blue. I've read comments to the effect that some feel the spirit matures better at that strength. Regardless, that hasn't always been the practice, and Diageo, for one, casked at full strength for some time, ostensibly (as noted) to make best use of warehouse space. Thus a number of older Caol Ila, Port Ellen, and Talisker cs bottles I've had were at 60% or more, including a Talisker 20 at 62.0%. I don't know how widespread this practice was, but maybe Convalmore did the same.
Bruichladdich now fill at full strength. The fact that they have no blending contracts may lend credence to my theory. Or not. But the higher filling strength may explain why Port Ellen, for example, has matured so well into its twenties. The lower strength may produce better results at ten to twelve years. Again, I'm only speculating.