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There has always been cycles where consistency suffers as a result of increased demand, the last 10 years have seen a huge increase in demand from China which has put pressure on the distilleries to increase production. Some distilleries are better at dealing with this than others, Glenlivet and Glenmorangie are notoriously bad at having any sort of consistency for their 12 year olds no matter what the demand is but Arberlour are an excellent example of a big distillery that always delivers what you expect.
My impression is that there's more variability between bottles of the same whisky these days than in the past - though i've no real evidence to back it up. I've kind of assumed that the majority of distilleries are increasing production, which results in some differences. I may just be making this up in my head though...