From Allen, “On the Composition of Some Greek Manuscripts”, p. 181:
To recapitulate the history of the MS. which we have now reconstructed; the sheets, numbered and ruled, were given out to be written. The scribe who received them wrote the text and the principal scholia in the places ruled to contain them ; during the act of writing he made corrections from time to time both in the text and the scholia. This done, he apparently began the book again and wrote in the irregular space left between the scholia and the text, and between the lines of the text, other shorter scholia in a different type of hand.
He took advantage of this opportunity to correct in an exhaustive manner the test he had written ; he added and altered breathings, accents and apostrophes, added and corrected critical signs, and wrote above or in the inner margin corrections of words. The book, thus complete in substance, was given to the original scribe who had numbered the quires and ruled the lines ; he compared it throughout with the archetype and noted on the edge of the page differences; sometimes he accompanied these with a mark to call attention ; he added lines left out, and omitted scholia either in the ruled margin or the intermediate space. In a few places he explicitly refers to his authority to defend himself from corrections already made in the text by, as it would seem, the first hand on his second round. Lastly, a third person reviewed in detail the suggestions of the reviser ; deleted a great number of them in favour of the reading in the text, and in other cases substituted a correction of his own. He added likewise omitted scholia and remarks of a general nature upon the context. This excessive carefulness in the preparation of the book is further seen in the numbering of the similes, the quantitative marks, and the supplements of the elisions.
The book was now complete. Its further history consists of the decay of its structure and the loss of its leaves.