Kuzen was an informal form of official document that came into use from the mid Heian period -- which was used by shikiji (administrative assistant) at kurodo dokoro (the Office of Imperial Household Logistics) (shikiji kurodo, kurodo no to - Head Chamberlain) or goi no kurodo (Chamberlain of the Fifth Rank) in transcribing the verbally received emperor's edict for conveying it to shokei (high-ranking court noble) at Daijokan (Grand Council of State). It had many parts in common with senji except for its form.
When the kurodo dokoro was founded after the Kusuko Incident in 810, the shikiji at the kurodo dokoro gradually assumed the role of conveying the imperial edict to the Daijokan -- the order had conventionally been conveyed by naishishi (also referred to as naishi no tsukasa; messengers from the palace attendants) at kokyu (the women's quarters of the Imperial Palace).
When the shikiji kurodo received the imperial edict, he took it to the jin no sadame (Council of State deliberation) and verbally conveyed it to the shokei. That was referred to as Oosekotoba (the words of His Majesty) given through the shikiji, also referred to as 'kuzen' (literally means stated by mouth) or 'senji' (literally means to state to that effect) because the order was verbally conveyed (verbally stated).
Nevertheless, the shokei was not always present at the Daijokan, which was why the emperor's side could have issued an extraordinary edict. That was why an error made by the kurodo or something happened in the process of conveying the edict might have resulted in a discrepancy between the order issued by the emperor and the order practically received by the shokei. For that reason, the custom was established to prepare the imperial edict on a sheet of paper in advance to be handed to the shokei.
That was shaped up into 'kuzen' or 'senji.'
This was the form of kuzen: Put the date of issue in the first line; then two Chinese characters '宣旨' (senji) on the second line from the date line; below the line of the two Chinese letters, the contents of the senji; and isho (the government post at kurodo dokoro, an additional post, and name) of hosha (the personnel who receive it) of the imperial edict, with a Chinese character '奉' added in a size smaller than that of the other letters. The form was established in the eleventh century -- When the kuzen began to be practiced (in the first half of tenth century), the form of kuzen had not been distinguished from the form of senji yet, and the date was put above the isho in the last line in some cases for kuzen. In order to make the shikiji, kurodo always prepared for the imperial order and because the imperial edict was entirely conveyed verbally and the kuzen was made just as a memorandum (memo), the custom was established using sheets of shukushi (also referred to as sukushi), which was simply made by recycling used paper -- That choice of paper formed a part of the document standards later on.
Incidentally, a Retired Emperor or a Cloistered Retired Emperor (so-called 'Chiten no kimi') who pulled the strings behind the scenes also used the kuzen for issuing an order to the Daijokan. Since legitimate government organs established by the Ritsuryo codes were the Emperor and the Daijokan, Chiten no kimi who had no legal basis had to use such an informal form of official document to issue an order.
Kuzen-an' was originally a draft proposal of kuzen, meaning no more than an incomplete version of a memorandum (memo); but later, it came into use as a means of directly conveying the imperial order to working-level officials, bypassing the Daijokan.
Various official documents for orders issued off the regular route were created until the Kamakura period, but exceptionally the documents for orders regarding personnel matters were created by sticking to the steps of issuing such regular official documents as an Imperial Rescript, the documents issued by the Daijokan, and the diploma of court rank. That was the same in the case where Chiten no kimi exercised his right of personnel management such that it was required to follow complicated procedures of putting on the appearance of an imperial order, conveyed to the Daijokan and further to the working-level officials. But from the tenure of Emperor Gosaga, in order to meet the requirement of conveying personnel change made by the Chiten no kimi -- who had the virtual right of personnel management -- to the official responsible for personnel matters as soon as possible, the shikiji kurodo who received the order issued by the Chiten no kimi (or the Emperor if under the personal rule of the Emperor) drew up a copy of the draft proposal of kuzen on the pretext of making an incomplete version of the kuzen and handed the copy of the draft proposal with inzen (document transcribed a retired emperor's order) of the Chiten no kimi who issued the kuzen (or a document transcribed of the Emperor's order) to the working-level officials, before submitting the kuzen to the shokei.
For distinguishing the copy from the script (original) of the kuzen, the three Chinese characters '口宣案' (kuzen-an; draft of kuzen) were written on the reverse edge and the so-called 'mei,' the name of the shokei to whom the kuzen was submitted, was added on the upper right of the first line of the copy before being handed over. Originally, it was arranged so that the kuzen-an was handed to the working-level officials and then the same order was issued by the Daijokan to the working-level officials -- Later, the step of issuing the order at the Daijokan was omitted, and the kuzen-an was considered to be the formal rescript.