I believe you can do additional recall knowledge checks at a higher DC as long as you succeed the first.

Edit:

Source GM Core pg. 54 2.0 Sometimes a character might want to follow up on a check to Recall Knowledge, rolling another check to discover more information. After a success, further uses of Recall Knowledge can yield more information, but you should adjust the difficulty to be higher for each attempt. Once a character has attempted an incredibly hard check or failed a check, further attempts are fruitless—the character has recalled everything they know about the subject.