Nice, but it's only available in English sadly, there's a link that says "see kalenderpuzzel "Ruit" for the Dutch version" (I'd prefer French but Dutch would do as well) but that page says "De maanden en dagen van de week zijn in het Engels".
The "square" one is in Dutch but sold out and the Rotterdam one in English only.
But I like that idea, apparently it's not the first puzzle of this kind but I didn't know about them.
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.
I thought the same thing, but it seems that certain dates would make it so there is one square ("rhombus") and one (non-square) rectangle (e.g. Feb 15).
So rather than 3 rhombuses – or 3 squares – perhaps it's 3 squares of 1 square and 1 rectangle. (Perhaps the positions of the puzzle pieces make it such that it truly is 3 squares)!
All dates are possible and most (all?) have multiple solutions.
The "square" one is in Dutch but sold out and the Rotterdam one in English only.
But I like that idea, apparently it's not the first puzzle of this kind but I didn't know about them.
https://www.youtube.com/watch?v=bccNH82DIo0
https://www.youtube.com/watch?v=hF_2yHXD_CU
(and...neat puzzle...nice job, creator!)
So rather than 3 rhombuses – or 3 squares – perhaps it's 3 squares of 1 square and 1 rectangle. (Perhaps the positions of the puzzle pieces make it such that it truly is 3 squares)!