Sentence:  ... the Chamberlains' records of the companies' visits to their towns are, for the most part, not precisely dates, but merely group them together ... within their annual accounting period which normally ... ran from Michaelmas (29 September) to Michaelmas, or its <WSD>octave</WSD> (6 October). 
Meaning of the word marked with <WSD> tags:  The day that is one week after a feast day in the Latin rite of the Catholic Church.