Early Song Historians - Secretariat & Document Drafting Office

Government of Early Chinese Song Dynasty Hello! I was hoping to have some clarification concerning the early Song dynasty, particularly the period prior to 1000, and I am hoping someone might be able to clarify a few points. I have been struggling to understand how the government system functioned during this era. The state operated under a Secretariat–Chancellery, a structure for which I have had difficulty finding clear, consolidated information over the past three weeks. I have consulted numerous sources, yet none provide a precise or consistent explanation of how these two branches functioned hierarchically or in relation to one another. From my current understanding, the Palace Secretariat (Western Office, civil, inner court) and the Chancellery were overseen by a chancellor (Counselor-in-Chief), and that the director-level position was abolished following the Tang dynasty. However, I have encountered multiple sources that list Tang-dynasty Palace Secretariat positions, making it difficult to determine which, if any, of these offices continued into the early Song period. From what I can gather, the Department of State Affairs operated beneath the Palace Secretariat. I also understand that, by this time, the Palace Secretariat had lost much of its former institutional authority, and many of the previous positions carried in the Tang Dynasty became honorary titles. Also, what exactly is the Document Drafting Office? I've found very little information relating to that anywhere. I'm wondering what purpose it served exactly, and why it was necessary to change to a bureau that does the exact same thing, just with a different name. I suppose it would've been difficult to tear down the original structure, but I feel like that makes things odd. That said, the material I have been working through remains vague and internally inconsistent, making it especially difficult to distinguish between the Tang-era Palace Secretariat and the form that existed during the early Song dynasty. I am currently working on a story, and it is with the best of intentions that I am attempting to sort through and accurately understand this. (Please ask for sources. I will provide one below, just as a base for the majority of information related to the questions I require to be answered.) ("When the Song dynasty 宋 (960-1279) was founded, the Palace Secretariat was deprived of its status and became an institution outside the imperial palace, like the Chancellery. Its function was reduced to the processing of certain less important documents, like memorials presented on a special occasion (cewen 冊文), resubmitted documents (fuzou 覆奏) or lists of official examinations (kaozhang 考帳). The office of the Counsellor-in-Chief was called Secretariat-Chancellery (zhongshu menxia 中書門下, short zhongshu 中書) or Administration Chamber (zhengshitang). It was located inside the Imperial Palace, and had nothing to do with the former Palace Secretariat. The latter had no director any more, and even the title of drafter (jilu guan 寄祿官) was purely honorific. Their duty was taken over by the drafters (zhizhigao 知制誥) of the new Document Drafting Office (sherenyuan 舍人院).")