Mike,
I got a few ideas about your bottle for you - Nothing exact, but should help narrow down the dating a bit for you!
I compared several ads showing bottles for KG-IV, and came down to two from 1912 & 1929, and noted similarities/differances below:
The Cap:
1912 - "Foil-wrap & Cork"
Yours - "Foil-wrap & Cork"
1929 - "Spring-Cap"
Bottler:
1912 - "Distillers Company LTD"
Yours - "Distillers Company LTD"
1929 - "Distillers Agency LTD"
Main-Label Description
1912 - "Liqueur Whisky"
Yours - "Scotch Whisky"
1929 - "Old Scotch Whisky" ("Gold Label" added )
Footer-Label Description:
1912 - "Special Quality"
Yours - "Special Quality"
1929 - "Extra Special"
Not an exact dating, but your bottle has more in common with the 1912 bottle than the 1929 bottle!
Since both Ad's straddle WWI, and war often having an impact on design changes, I'd suggest trying
to find some examples from about the early 1920's as the potential 'best bet' to finding a match here.
Cheers,
Walter C Hurst
wchurst@hotmail.com