Indeed, if there were not already a line written below the inserted emendation, there would have been no reason to condense the letters and spacing of the inserted phrase; nothing would have demarked the space available for the insertion.
This is the part you highlighted, but it is pure nonsense. No reason you say? As I already illustrated above, if this were a dictation scenario, then there would be a reason. But since you reject the dictation scenario, that leaves you without one. Again, your problem isn't lack of evidence, but your failure to account for it.
As I explained, the scribe transcribing the dictation would expect there to be an upcoming line below the text. You have not adequately accounted for the line above which crashes upwards. Why does this happen? You don't say.
The insertion of "commencement of this record" was placed in the appropriate gap in order to return the transcription to a balanced format. I've done this on plenty occasions when writing on sheets void of lines. Notebook paper contains lines to help keep the writing horizontal. The scribe clearly filled in the huge gap for the purpose of smoothing the text out and recommencing with a perfectly horizontal line.
His only other choice was that he could have continued writing all subsequent lines parallel to the screwed up line above. That would have resulted in a mess of a transcription.
Simply put, writing on paper without lines makes it easy to drift up or down. A distracted or less than diligent scribe could make this mistake easily. Once the mistake is made, it makes perfect sense to account for it. This seems to be the purpose of the phrase inserted the in this manner.
Anyway, I'll let you two get back to business.