The holograph of the Kitāb-i-‘Ahd is now preserved in the Archives at the Bahā’ī World Centre. No further information as to the circumstances of its revelation, editing or publication is currently available to us that cannot be found in published accounts. As can be seen from a comparison of the English translation authorized by the Universal House of Justice with the published Persian text, a reference to the wife and family of Bahā’u’llāh (‘ḥaram va āl allāh’) has been rendered collectively as ‘members of the Holy Household’. The holograph of the Kitāb-i-‘Ahd contains a passage in the nature of a postscript praising Mīrzā Ākā Jān, directing the friends to show respect to him and expressing the hope that he join ‘Abdu’l-Bahā in upholding the standard of loyalty. The postscript was not included as part of the Will by ‘Abdu’l-Bahā when He circulated it during His lifetime, and this approach was continued by Shoghi Effendi. The House of Justice, likewise, has decided not to circulate it.
-UHJ, source: https://bahai-library.com/pdf/b/buck_ioannesyan_russian_will.pdf, pp. 39-40
This seems to correspond with the version by Mirza Muhammad Ali:
After the said followers heard the will and left, Ghusn-i-A‘zam sent for me from where I was sitting in the adjoining room and then for the first time I read the will of our Great Father Baha’u’llah. I observed the last part of the will was covered with a dark paper so that no one could read it. But as I raised the will to read it, which was written on two pages, the dark paper which was not stuck slipped. Ghusn-i-A‘zam said, “It shall not be a secret from you, only I do not wish as yet that the believers should read it and know its contents [i.e. the hidden part].” I read it all, and it (i.e. the part covered) was regarding Khadim and his services, and at the end addressed both Ghusn-i-A‘zam and the Khadim enjoining them to be faithful to Him. (…)
The hiding of the last part of the Book of My Covenant caused me uneasiness and great surprise, as a will is written for being spread and for carrying out its contents, and hiding it is contrary to the intention for which it is written. But under the circumstances I kept silent and did not raise an objection, hoping that later on it (i.e. the entire will) would be produced and the station of Khadim ordained in the will be made known, so that Baha’u’llah’s wish in this respect be known to everyone, and that all may know that none shall be deprived of the recompense of their services, and the forty years service of Khadim be not lost and considered as vain.
This incident is mentioned as well by Mirza Aqa Jan and Mirza Jawad Gazvini. In the 1930s did Mirza Muhammad Ali state the contents of the hidden part referenced the station of Abdul Baha and Mirza Aqa Jan. 80 years later this was confirmed by the UHJ.
How can they decide which part of the will of Baha’u’llah can be published and which be forgotten? The point of a will is that everyone knows the deceased person’s final wishes. Why won’t they publish it?