Kumku, glossed as granary, is the last of the eighteen full months, and it has a prominence out of proportion to its position because the Maya creation date falls in it. The Long Count starting point, 13.0.0.0.0 in the previous era, is recorded on Classic monuments as the day 4 Ajaw 8 Kumku, and that phrase appears wherever an inscription reaches back to the beginning of the present world.
A Calendar Round date such as 4 Ajaw 8 Kumku does not by itself identify a unique day, since the pairing recurs every 18,980 days. It is the Long Count that fixes it. Classic monuments habitually give both, and the redundancy is what makes the correlation of Maya dates with the European calendar possible at all.
A Maya date does not name a month and a number in the way a European one does. It names a day in the 260-day Tzolk'in, by number and sign, and a position in the 365-day Haab, by day and month, and the two together form the Calendar Round, which repeats only after 18,980 days, a little under fifty-two years. Within the Haab the days of a month are numbered from zero to nineteen, and the zero day is not called first but seated, the seating of the month, a usage the Classic inscriptions write with its own glyph.