At
http://www.ne.jp/asahi/miniature/smallw ... urbonk.htm is a collection of mini whiskey bottles. His collection of Kentucky Tavern shows 5 bottles from different eras. The dimpled bottle shown in the thread above seems to be similar to the Japanese site's bottle from 1947, however that site's bottle shows 100 proof. So do his 3 other bottles marked Bottled in Bond. While it is hard to read the labels, in his table just underneath he states the proof as 100 in each case. Only the fifth bottle pictured (from left to right) shows a lesser proof, 80, and it is not marked Bonded.
My conclusion is that the bottle pictured on the BE thread above, which ended up in England, was marked to comply with the proof requirements of the day in the U.K. and 86 British proof was essentially 50% abv. which was and is American bonded strength. Another reason I think that is in photos of American whiskey bottles I have seen in U.K.-published books from the 70's, again we see lower proof markings on some bottles than was current in the U.S. at the time, e.g., I saw a Jack Daniels bottle marked 78 proof which is 90 proof in the U.S., which JD was at the time.
Alternatively, the Kentucky Tavern bottle may have been 86 U.S. proof but the manufacturer left the Bonded statement from the U.S. bonded bottle design on on the basis that it might have some selling effect and since the bottle was sold outside the States such usage did not contravene any rules. But I think the former interpretation makes more sense.
Gary