Recently I designed a calendar puzzle with 10 tetris-like pieces. When you place all the puzzle pieces on the board, three squares/rhombuses are still open and together they form a date. Can you arrange the puzzle pieces in such a way that it shows todays date? See https://praxispuzzles.com/calendar_puzzle_rhombus Disclaimer: I sell these puzzles for a little more than the raw material.
You are right. This puzzle started my search into this type of puzzle. But in the end my puzzle is harder, because it also contains the day of the week and has the most "irregular" puzzle pieces possible.
You can arrange the puzzle pieces to make dates that don't exist, like Monday February 31. Actually there may be "impossible" dates, because I didn't check for them, but I think all combinations of days of the week, day of the month and month are possible.
