Author mistake, Maybe??

[graniteworks at sbcglobal.net]

No: HPFGUIDX 55444

Did you ever notice that in HP&SS(#1) at the welcoming feast in the 
beginning when Harry and Ron first meet Nearly Headless Nick, the 
Gryffindor ghost, Nick states that he hasn't eaten anything in almost 
400 years but in HP&CS(#2) Nearly Headless Nick has his 500th death 
day party? He seemed to have jumped from 400 years dead to 500 years 
dead in one year. Do you think that that is just a mistype or what??? 

"graniteworks"