This add-on recognizes when someone joins the guild and, if you have the rights to write in the "Officer's Note", it will add the date in the format "Month DAY, YEAR".
Since the Player isn't added at the same time as it is said in the System chat, there is a delay of 3 seconds between the "has joined" message and the writing in the "Officer's Note". This lead to a simple "bug" when 2+ people accept the guild invitation at the same time. Another issue is that if the player log out before the 3 seconds, it might not add it in the Notes either.
These 2 issues might be fixed if the WoW API allows it at some point.