When you do something in your nth attempt the last one is still included in the number of attempts. The reason for the different rubrics is to differentiate between failed and successful attempts (difference in scale between actually murdering someone or trying and failing to do so).

yeah, you can speak about "attempting" to do something before knowing the outcome, so i don't think failure is baked in. i can't really speak to the legal concept.

but the book also includes the lincoln assassination. i guess a book of only failed attempts was too thin even for a lego history coffee table book, so they had to pad it out a bit with the successful ones.