An example, probably starting not so long ago, includes the last 500 (9)
I believe the answer is:
precedent
'an example' is the definition.
(precedent is a kind of example)
'probably starting not so long ago includes the last 500' is the wordplay.
'starting' indicates taking the first letters.
'not so long ago' becomes 'recent' (I've seen this in another clue).
'includes' is an insertion indicator.
'last' suggests the final letters.
'n00' becomes 'D' (Roman numeral for n00).
The first letter of 'probably' is 'p'.
The final letter of 'the' is 'e'.
'e'+'d'='ed'
'recent' enclosing 'ed' is 'recedent'.
'p'+'recedent'='PRECEDENT'
(Other definitions for precedent that I've seen before include "Earlier parallel event" , "Past instance serving as example" , "case one may need to quote" , "An earlier example serving as a guide" , "Decision to return to" .)