Wonderful Gencer, always full of surprises. I attended this concert, it was in July 1989 at Aya Irini in Istanbul. I believe she had given a smaller concert at the Bosphorus university the evening before. She was very tired, but still gave an encore. Missing from this video is her wonderful "Sposa, son disprezzata" from Bajazet. She sang in public only once or twice more after this. She was at least 65 years of age (her "official" birth year is wrong...as confirmed that evening by an older gentleman who had been in school with her).
I am sorry to say this - but Leyla Gencer has not only mere intonation problems here. She seems to sing in an entire different key as the orchestra for long stretches. Fron the visuals I understand, the this must be very, very late in her career. Still I find this no excuse for that kind of flat singing.
She was old. and tired because of the concert she gave the night before. A retired singer... You are right but she had excuses. Her angelic voice however, still gives me goosebumps anyways.