OK, lets say the last day of any month ended on a Wednesday, the build date of a car built that week through Wednesday would be MMd or e (depending on the number of weeks in that month, partial or whole). The cars built the next day(Thursday, 1st of new month) would be MMa. So in answer to your question 11A would be just for the one day(November 1st) and 11D would be the 18th - 22nd. IMO