Jashodev chatterjee: Please accept my humble obeisances. All glories to Srila Prabhupada. I have a question which I will be very grateful if you could kindly answer.
It is:
Q) Please refer to the article: Was Shrila Prabhupada a Prophet? Read His Letter to Gandhi and See for Yourself! by His Grace Patita Pavana das Adhikary. How do we know for sure that Srila Prabhupada did indeed send such a letter to Mahatma Gamdhi? Did Prabhupada keep a copy with himself? Did Gandhi’s secretary or someone like that hand over the said letter to ISKCON? Can we verify by empirical means that indeed such a letter was sent to Gandhi?
Your aspiring servant jashodev

The letter is featured in the first volume of “Srila Prabhupada Lilamrta.” Srila Prabhupada must have kept a copy.
I seem to recall seeing a photograph of a copy of the letter. I am sure that Bhaktivedanta Archives could provide an answer that would satisfy your curiosity.