Some proofs from Srila Prabhupada that the Macmillan 1972 edition is the “only original” edition
There is the report from the trade manager of Macmillan Company. He says: “While other editions are dwindling, going down, this edition is coming up.” They published our this present enlarged edition of Bhagavad-gītā, fifty thousand in the month of August. They are going to print again, second edition, August, September, October. So the reason is that if we present things as they are, it will be accepted. Without any adulteration.
Sometimes, you know, people say that I have done miracles. They say everywhere. But I do not know anything miracles or magic. If there is any miracle, that miracle is that we present things as they are, that’s all, without any adulteration. So that should be the principle. Present as it is: it will be accepted. [Lecture SB 01.02.11 – Vrndavana,October 22, 1972]
They even rejected Radhakrishnan’s Gita, which shows that this is the original edition that Srila Prabhupada wants. He also says “real thing will have real value”, so we know that the 1972 edition is the real copy.
Prabhupāda: Yes, let me finish, that . . . We are presenting Bhagavad-gītā as it is, and it is being accepted all over the world. People are very much, those who are scholars, they say that even Radhakrishnan and Aurobindo, they presented Bhagavad-gītā, making some compromise with the Western ideas. But here is presentation of Bhagavad-gītā in India’s original, traditional way. So they welcome it. And this is our, I mean to say, object also, that we cannot allow Bhagavad-gītā to be understood by anyone’s imagination. No. That is not possible. And that is not allowed in the Bhagavad-gītā by the author. Kṛṣṇa says in the Fourth Chapter that as soon as the paramparā system of understanding is lost, then the whole thing is lost. In the Fourth Chapter it is said. (aside:) Find out Fourth Chapter. [Interview-CHANDIGARH – October 16, 1976]