I'm surprised they put Hebrew on there. Who donated that didn't understand Yiddish or English?
It was probably just convention. Yiddish was for understanding then; only Communists had turned Yiddish into a hailige language by that point, so it probably just didn't make sense to have an official multilingual receipt from a yeshiva without Hebrew.Note: this receipt was obviously for Americans (and Brits, maybe).
At what point did the yeshiva add 'Chofetz Chaim' onto its name after the book written by a local?
Better people than I could answer that, but I think you're making a mistake. The Radun yeshiva was always the Chafet'z Chaim's yeshiva, I think. Obviously if it was founded in 1864 it could not have been called Chofetz Chaim at least until he gained fame under that name, so your question is perfectly fair.Also, unless the 70 years is not literal, then this receipt is from 1934, that is after he died. One wonders if they were issuing such a receipt before his death, complete with his facsimile signature - can you imagine today a rosh yeshiva explaining himself in that way in fundraising material? Of course since they don't indicate in any way that he is deceased, perhaps it's not literal and it could be as old as 1930 or even a little older.
We've got a bunch of letters from the secretary of the yeshiva from about 1934. I think they all say "Chafetz Chaim" on the letterhead.