Crossword puzzle clue "one is in each theme entry"

Like each answer in this puzzle - also each word in each clue - in length

There's one at the beginning of each theme entry

Today, I tried to put a self-effacing three-letter acronym inside each theme entry. Turns out it works in any order except the one I want. ___

The beginning of each theme entry is one

One is in each theme entry

There's one in each theme entry

Theme answer count, amount of letters in each, word hidden in each, and, when repeated twice, today's date

Word that can follow the last word in each theme entry