Reagan was the only President to survive that long after being shot, yes, that is true. However President James A. Garfield was shot by Charles J. Guiteau on July 2 1881, four months after his election as the 20th U.S. President. Garfield died 11 weeks later on Sept. 19, 1881.
The shooting was witnessed by Robert Todd Lincoln, one of President Lincoln’s sons, who had already gone through this experience years before, of seeing history being violently made. One bullet remained lodged in Garfield’s body. The doctors probed with unsterilized fingers and instruments, but could not locate it. Alexander Graham Bell devised a metal detector specifically for the purpose of finding that bullet lodged inside Garfield, but the metal hospital bed he was lain on made accurate detection impossible.