Some things I don't understand about "Tale of Locker 22:"

1. No one else was assigned locker 22 between all those years of Candy's death and Julie coming to the school, why exactly? Presumably that was why Candy appeared to Julie, because they shared the same locker. If it was assigned to another student between Candy and Julie's times...you know what I mean, right?
2. If Candy hadn't shown herself to anyone before, how was there even a rumor about the school being haunted? How did the other student Chris mentioned see her?
3. Mr. Adam said Candy "got careless." How was Chris able to figure out it was due to Mr. Shaffner being careless? And, shouldn't the truth have been discovered after the explosion; in that case, how did Mr. Shaffner even keep his job as a teacher, let alone become assistant principal?
4. A common discussed theme is the butterfly effect. It is said that everything happens for a reason, and if even the slightest thing in history was altered (even with good intentions)...again, you know what I mean. Yeah, I'm thinking too much. LOL