Why do notes not add up to the bar in this example by Couperin?

Question

Consider following excerpt from the beginning of Couperin's Leçon des ténèbres pour le mercredi saint:

I noticed that the note values don't always add up in a bar.

Cases (indicated in the figure):

1. The five 1/128th notes do not add up to an eighth note. Should they nevertheless occupy the total duration of an eighth note?
2. The 4 notes (EDCD) can be seen as an accacciatura to the next beat (the E in the next bar). They are notated superposed on the half note D that occupies one beat of the bar. This is correct notation, but I would use 16th notes instead 8th notes because four 8th notes equal one half note, leaving no time for the half note D.
3. This is a common case where the triplet "3" is not mentioned.

I can understand the cases 2 and 3, but why would one notate the case 1 in this way? I guess tuplets where not yet used at the time? He could have written the dotted quartet E as a half note and superpose the five 128th notes just like he did for the case 2.

Answer 1

In Couperin's time, a dot after a note-head didn't always mean to extend the duration by exactly 50%. Here, each dot means to extend the duration by just the right amount so as to make the durations in the top line match the bass.