Trying to understand Class >> category

Hi guys. I need a category expert to explain why we have the following:

Class >> category

"Answer the system organization category for the receiver. First check whether the

category name stored in the ivar is still correct and only if this fails look it up

(latter is much more expensive)"

| result |

self basicCategory ifNotNil: [ :symbol |

((self environment organization listAtCategoryNamed: symbol) includes: self name)

ifTrue: [ ^symbol ] ].

self basicCategory: (result := self environment organization categoryOfElement: self name).

^result

So...how can a class store an "incorrect" category?  

Or in other words.... can

use #basicCategory (simple accessor) rather than #category? 

thanks,