Bullets shouldn't fly far enough to kill enemies off screen. For the signs, which section of the level was it? Because there are sections in which you need to destroy the signs by shooting them. Could that be the problem?
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the part where these start appearing: https://img.itch.zone/aW1hZ2UvNDMwNjU5LzIxNTg3ODcucG5n/original/BWgBNy.png