I have written many times about Mirza Ghulam Ahmad and his team of writers.  I continue to find more and more data on this topic.  Recently, we have the following references:

The quotes

“His holiness, the Promised Messiah, wrote his book of Tabligh, which is included in his book Aina-e-Kalamat-e-Islam in Arabic. During the course of its writing, he used to send the manuscript to the philosopher of the community, Nuruddin, for proof reading. After this, he used to send it to ustad Abdul Karim so that he may translate it in Persian.”
(Al-Fadl, January 15, 1929)

“His holiness (Mirza) used to send manuscripts of his Arabic books to his first Caliph (Nuruddin) and also to Ustad Mohammad Ahsan. The first caliph used to return the manuscripts after reading them, mostly as he took them. As for Ustad Muhammad Ahsan, he exerted his utmost effort and at some places used to change words for correction.”
(Seerat-ul-Mahdi, Vol. 1, P. 91)

Mirza Ghulam even asked others to submit articles to be included in his book. Here is a letter Mirza composed to Chiragh Ali:
“I have been much pleased to receive your letter. From the very beginning, it has been my desire to serve Islam. Your book has encouraged me tremendously… If you have any articles, send them over to me… Your article about confirmation of prophethood has not reached me so far, although I have waited for it long. Therefore, I bother you once again to send me your article without delay. I would like you to write another article for me about affirmation of the reality of Quran, so that I may be able to include it in my book Baraheen-e-Ahmadiyyah.”
(Seyar-ul-Musannifin, Letter to Chiragh Ali;
As reported in Qadiyaniat-An Analytical Survey)

The scans