Giazottos Albinoni Adagio

One of the most played works of music, but the author Remo Giazotto insists that he merely arranged it based on a yet undiscovered fragment of Albinonis. Someone knows more about this? It's kind of fascinating that someone who could very likely take credit for a insanely successful piece of music, doesn't. Did this supposed fragment of an Albinoni bass line turn up at some point?