Most whiskies consumed in the world are blends: as much as 95 of 100 sold whiskies are blended whisky.
A blended whisky is a whisky that is the result of vatting together several single malt whiskies and some grain whiskies. The job of vatting together the whiskies choosing from a huge amount of distilleries is done by the Master Blender. Some brands are about creating an artisan whisky and some other brands are about getting a cheap booze drink.
So a Master blender, choosing from a set of malt and grain whiskies, has to ensure that resulting whisky is better than its individual components. Usually this tasks consists in the combination of 15 to 40 whiskies done according to a secret formula that each brand vary. There are light whiskies like J&B or more robust and complex like Johnnie Walker.
Master blender nose whiskies all along their maturation period until whiskies are mature and ready to use in the blend. Selected whiskies are then bring together, pumped in a vat according to a given proportion and finally back to casks were they take the final maturation period know as marriage. Not all brands do marriage.
Age in the label statement of a bottle is the age of the youngest whisky added into the blend. Many brands opt for a no age statement as a way of ensuring that they are not limited by age when choosing great whiskies to make the blend. Others just have no age statement because mayor part of the whisky is a cheap light grain spirit with no flavour used to make the blend more light.
So after marriage, whisky is nosed again to ensure that it reach the required profiles expected by the brand and reduced to drinking strength ( usually 40% alc. ) and then bottled.
All the Scotch whisky have to be distilled, matured and bottled in Scotland. It is not strange anyway to see whisky distilled in Scotland and later blended and bottled in another country.