A quick Google supplies the answer that Glen Crannog is a vatted malt that is the own-label such malt produced by Threshers/Haddows (are there national chains of off-licences, i.e. booze shops, in N America/Australasia?), with Chieftain's likewise from an independent bottler, Ian Macleod Distillers, which, to my shame, since it was founded in 1936, I've never heard of before. And, BTW, they're none the worse for being vatted malts,- Green Label is also such a malt!!
For an explanation of what is a "vatted malt", - see http://www.maltmadness.com/guide-02.html for a good explanation. This and the other 9 chapters of this beginner's guide is one of the best I've come across.
Note to self: must check on the age of that cask of mine sitting in Campbeltown. The previous one gave a very nice return on investment! and a few bottles of a superb Springbank
David