The Buddha responds that this dharani is difficult to encounter and that even the innumerable Buddhas do not know where it is gained from. And later on, the Buddha recounts how in the past he went to meet innumerable Buddhas to find this dharani but was unable to until he met a Buddha who received the dharani from Guan yin in the distant past. Because of this I have some questions:
I am not familiar with the Sutra you mentioned. It seems to be from the Pali canon which is different from my source of information: the Sanskrit canon.
Furthermore, I am not sure about the accuracy of the translation. I was very lucky to learn from English translations of Mahayana that were certified by my Chinese Master, Ven. Xuan Hua.
Allow me to briefly offer my humble and limited views: