Not sure if its treated the same with nclex, but on other board exams, passing is 80%, and theres a minimal score that if you drop below throughout the testing process, thats where itll cut you off regardless of how many questions in you are. 265 seems to be the max, so if even if you fumbled on a few questions, as long as you were above that critical pass value, and made it to at least 80% by the time you've hit 265 you've passed
Whether you pass or fail the NCLEX depends on your questions being above or below the "passing line". If you have 265 questions, the last question determines if you pass the exam. If the last question (whether you get it right or wrong) is above the passing line (i.e. a difficult question) then you've passed. If the last question is below the passing line (again, whether right or wrong), you've failed the exam. The latest stats show that those who pass the exam get approximately 54% of their questions right, with the majority of them being above the passing line.