I have one more question. Is it possible to complete every level in the game without using the replacement tiles on the right? It has seemed possible on every level I've played so far except the first one.
Good question! Some puzzles were designed with known solutions, surrounded by random tiles, while others (mainly the maps I worked on!) are entirely random tiles, with generous replacement reserves so we don't soft-lock anyone. For the latter set, then, whether or not they can be completed without replacements changes with every playthrough. With more time, a known replacement-free solution for every puzzle would be one of my design goals.