Penguin had done weird stuff typographically. And now I understand why.
In the back of the book is a "List of Variants", which details minutely what manuscripts have been used. I mean, important stuff like "La" vs "la".
And they list these variants based on page and line numbers.
This was done for the previous, un-annotated edition. So when they wanted to add some footnotes, they either had to re-do the entire "List of Variants", or do it the easy/hard way by just pasting in new lines (in a narrower typescript) here and there.
It's all so logical.