You can use calendar notes to keep track of why you've blocked dates on your host calendar.
To block dates and add a note, follow these steps:
Select the date range to want to block on your listing's calendar
Toggle the availability switch off (dates will turn grey)
Go to the NOTES field and add your note
Select SAVE and you'll see a note icon appear on those dates
Select the note icon to read the note
Keep in mind, you can only add a not to an unavailable date, and marking the dates as available again will remove any notes.
Each date can only contain one note, so if you add a note to a date that already contains one, the new note will override the previous.