[Hieronymus]

If my memory serves me correctly, Octaves took two big hits in the 20th century, one under St. Pius X and one under Bl. John XXIII. That said, as we are dealing with a time prior to the standardization under St. Pius V, it would be difficult, and perhaps impossible, to ascertain the details of the calendar used in the French court.

[Verginius Rufus]

I don't understand what the difficulty is. The western European countries were all using the same calendar and November 1 was the accepted date of the feast of All Saints (apparently in earlier centuries it had been on different dates at least in some parts of the Christian world). The Monday after All Saints can be easily calculated.

The octave has to be the eighth day (counting inclusively so Nov. 8 is the octave of Nov. 1).