Maybe I'm missing something, but TO ME, it looks like 21 has 5 solutions:
https://files.catbox.moe/5vha7t.webp
The attached image illustrates my reasoning.
Viewing post in Hatsune Miku Bomb Squad! comments
You're not wrong, this puzzle was actually a last minute addition and probably had less overall testing.
That said only one of the proposed solution in your document has the full context to fill out from the clues available. All the others require some sort of guess.
This still breaks the conventions I set elsewhere, so definitely not ideal.
I mean... I see what you're talking about, but that doesn't mean anything for a player trying to reason through a puzzle.
Because - speaking as a player - the logic I employed could be described as... "I should put this hint here because if I put it somewhere else, it doesn't work".
And if it does work, I assume that I'm on the right track. Maybe I'm the only one who thinks this way, but I'm not going to backtrack if everything fits but I don't have the full context. I'm just going to guess. Because I'm logically assuming that if I guess wrong, I'll just arrive at a solution that doesn't work in some fashion.
This logic does rely on the assumption that there is either only one solution available, or any correct solution will be accepted. An assumption that pretty much every player would have. So the situation is indeed not ideal.
It's a cool game though!
Yeah I am in agreement, but sadly the genie is out of the bottle. With how many downloads the game received I would be hesitant to release any patch for a non-critical error since most people will not manually update.
This is definitely something for me to consider should I ever make a sequel or large scale expansion. In my mind it feels I have a few options.
1) Create flowcharts like yours to ensure every puzzle has no forked solution tree. Which is fair amount of work, but doable.
2) Design additional levels like this and have Miku explicitly mention "A bomb squad member never guesses, the correct solution will always have full context" however I doubt most people will read what she says.
3) Add checks for multiple orientations of symbols for puzzles like this, which is again a fair amount of work, but doable.