The heading contains the date of 1580 but section V states 1646. Is there anything in sections I to IV that is inconsistent with the date of 1580? Could sections II to IV be somewhere in between the two dates? Your thoughts are welcome!
I think that sections I to IV should be considered as one, i.e. all from the same date (1580). The last section was added in 1646.
If one or more sections between I and V were added at another time, the new date would 've been stated the same way as in section V.