This singer has always been one of my favorites, since the first time I heard a recording of him 'way back in the early 1980's,
He never sang badly. He never had an 'off' day.
One story I remember hearing about him: the great tenor was asked about warming up before going on stage, what did he do, how long did he warm up, etc. The great tenor said --I test the voice, perhaps sing a scale, not more. If the voice is there, it's there; if not, there's not anything anyone can do about it.
From all accounts, the voice of Jussi Bjoerling was always "there".