Syndicate 58/6 Single Malt Glenglassaugh 24 Year Old

Hi,

Came across this bottle at a Whisky exhibition in Japan and wondered if anyone had any background info/knowledge on it?

http://ozakitrading.cool.ne.jp/single/single.html (the bottle on the right)

It's a single malt, Glenglassaugh, distilled in 1983 and aged for 24 years. Whislt I've seen plenty of references to Syndicate 58/6 blends, I've never come across any single malts under that brand. Did Syndicate 58/6 at one point bottle individual casks that were originally intended for blending?

Thanks