Deathday - 100 years discrepancy

[jlh_hp]

No: HPFGUIDX 69247

First post.  How did I go all this time not knowing this was here?  
I just started re-reading PS/SS, after finishing OOP.  I have done 
this several times with the first four, while waiting for OOP.  
However I never noticed the discrepancy between PS/SS on p. 123 
Nearly Headless Nick says "I haven't eaten for nearly four hundred  
years".  Then in CoS p. 129 Nick says "Well, this Halloween will be 
my five hundredth deathday".  How did Sir Nicholas leap forward 100 
years between Harry's first and second years at Hogwarts?  I have 
tried searching for "deathday" but don't see this topic anywhere.  
If it is an old topic, please just send me to that thread.  Thanks!
 ~ janna ~