Intro
Roughly 9 months after becoming the Khalifa, Mahmud Ahmad and his team of Mullahs began responding to the Lahori-Ahmadis.  This book was written in response to Kwaja Kamaluddin’s book which had been published a few months earlier in 1914.

Mahmud Ahmad’s error
He was debating the prophethood of MGA with the Lahori-Ahmadis.  Mahmud Ahmad explained that MGA’s prophet started after 1902…after the publishing of Tiryaq-ul-Qulub, however, he later changed his story and landed on the “Correction of an Error” announcement in Nov-1901.

Al-Qaul-ul-Fasl, published on 30th January 1915, Mirza Mahmud Ahmad wrote:

“In short, the reference quoted above proves that until the publication of Tiryaq-ul-Qulub, [the writing of] which began in August 1899 and ended on 25 October 1902, his belief was that he has partial excellence over Jesus and that his being called prophet means a kind of partial pro­phethood and deficient prophethood. But afterwards … he learnt from God that he excels the Messiah in all qualities and is not the recipient of any partial prophet­hood, but is a prophet. … Thus it is absolutely unallow­able to use any writing before 1902 as evidence because the Promised Messiah has given the decision that, as regards his belief about prophet­hood which he expressed in Tiryaq-ul-Qulub, later revela­tion made him change it.” (Al-Qaul-ul-Fasl, p. 24. This book is on their website http://www.alislam.org in the collection Anwar-ul-‘ulum, v. 2, book no. 8. See page 285.)