dnd 3.5e – Knowledge checks to identify creatures?

In SRD I read

Try again

No. The check represents what you know and think about a topic
The second time it does not let you know something you never learned in
The first place.

The question is, how often can a knowledge check be done to identify a creature?

Once a meeting?
Once every time a new creature appears?
Only the first time you meet a creature?
Can you try again when you gain a rank?

A couple of examples
Some undead appear. The cleric fails his knowledge of his religion.
a) After a few rounds, more of the same type join the match. How is this handled?
b) The cleric never grows his knowlage (religion), but a few days later he meets the same monster. Can the cleric make another check?

Thank you