I was checking out a dusty scotch bottle of "Old Rarity" from the 1970's. It is labeled as 12yo, 86 proof, and on the back label states "Blended Scotch Whisky", "100% Scotch Whiskies".

The actual meaning of this wording seems to change over time, so in this time period, what does this mean?

That it is all whisky distilled in Scotland, some of which is GNS?

Or is it what used to be called a vatting, where it is a blend of single malts?