Others just used the year of issue, while others used only the year of expiration. Indeed, if you are using the directory as a springboard to other records, such as census or vital records, you should learn the month when it was issued. The important information to determine is when the directory was canvassed. The information can be no more recent than the canvass. If a man is listed in one directory, and his widow is in the next, you want to know when he died, and it was between the two canvasses.
Most directories seem to have had a creation cycle of about one month.
Often this information is found in the publisher's preface or introduction. Back to Top Breadth of Search Search every year for which you can find a directory. This is one of the benefits of using a microfilm collection, rather than the sometimes-spotty collection of a local repository. It is amazing how much our ancestor's families changed in a relatively short period of time. Sometimes an unknown relative will be living with a known family member, and will be so indicated by having the same address.