Hey thanks for playing and the in-depth review!
The Starter Crown and Wonderland Crown are only different in aesthetics... The in-universe explanation would be the company selling Ludochess sells a tutorial "Starter Pack" for new players, which includes the Starter Crown and 5 copies of each Starter piece (cut to 2 for the jam, so the box is not too cluttered). Then whenever they release a new series of pieces, they come in the form of collectible blind boxes, and a crown to match the theme is sold on the side.
But since I didn't get the time to implement tournaments (where you earn prize money and possibly limited edition blind boxes preserved for specific tournaments) or the store (where you buy blind boxes, crowns and perhaps differently colored bases), I just provided players two of each piece to play with. But I do plan to add them in if the game gets a good overall reception ;)