There is a previous answer to this question given by u/savvysioux here: https://www.reddit.com/r/AskHistorians/comments/53sxwl/was_the_millennium_from_9991000_ad_marked_in_any/d7y708j/

Follow up question: How aware of the calendar year would the average peasant in that time have been? I assume they would generally follow the days and months but may not be aware or diligently keep track of the years.