Well, the info I got was from musicians who knew him, and loved him, and had no axe to grind. So I accept it at face value. People think that little tidbits like that are meant to demean, when in reality they are just facts of life. Some artists do their best work when they're "sauced," and if that's what it takes for them to get the job done, then I say "Bottoms up!" In any case, and for whatever reason, I don't accept apologists like Kennedy being "surprised" that there were so many good performances. It's insulting to any artist of stature, and so typical of a certain pathetic attitude prevalent in the arts ("We're so wonderful that you should love us even for our faults,"--or some version of the Romantic notion of an artist literally giving their life for their art, damn the audible consequences). There is nothing noble in mediocrity. Barbirolli was a professional, and his best performances show he had high standards, and so certainly knew, or had he ability to know, when he was doing his best and when he wasn't. I think that giving him credit for this basic perception is far more respectful of his achievement than making excuses for his failings. Admittedly, the material offered recently from the likes of sub-fusc labels such as BBC Classics is unauthorized (by him) and likely would never have been permitted to be released had he still been with us, but at the end of the day there is no justification, ever, for doing poor work. From a personal point of view, illness or badly fitting teeth may be regrettable, but a bad performance from a technical point of view is inexcusable.
Dave H