Came across this ad from 1907 on Ebay
Curiously it is advertised as a pure pot still.
- Old Bushmills Pure Pot Still 1907 Advert
- BushmillsAd1907 - Copy.jpg (37.3 KiB) Viewed 983 times
I think this is more trying to emphasise that is was not a blend but a pure potstill malt.
One has to remember that single malt was not really a term back in those days.