Creator here. No, 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 guess all combinations of days of the week, day of the month and month are possible. And also many non-dates, like 1, 2, 3. But good point: alle possible dates have at least 1 solution. Disclaimer: I sell these puzzles for a little more than the raw material.
I wrote 2 solvers in Python. One that loops through all possible dates and searches for a solution. And one that loops through all solutions and checks if they form a date or not. And luckily both gave the same answers.
Actually I tried a lot of different combinations of piece shapes to find the "hardest" set of pieces that can still solve all possible dates. "Hard" is subjective, but I mean pieces with multiple protrusions.
