I'm currently reading Yeast and I think I read something on this last night. If I'm not mistaken, the authors says that the high alcohol content makes it difficult for the yeast to wake back up. A suggestion offered was to make a starter and pitch at high krausen. The theory goes that with the yeast already active, the newer batch has a fighting chance at fermenting out. Their example was for a stuck fermentation that was only a few points away though. I'll check after work to make sure the info is correct. Anyway, it seems you got it back going again anyway, so Cheers!