Adding to your collection
Looking at the catalogue
A date consists of day, month, and year. If the day is unknown,
it will have a value of 0, likewise for the month.
The year must always be in 4-digit form.
At the moment, the date formats are dd/mm/yyyy and mm/yyyy.
Date ranges are also allowed, such as when filtering stamp types. You can do a year range as YYYY-yyyy, or abbreviate with fewer digits if possible. For instance, "1870-2" specifies the years 1870, 1871, and 1872 inclusive.