How Do CPR 31

How do CPR 31.16 (pre-action disclosure) and CPR 31.17 (disclosure against non-parties) differ?

A) For CPR 31.16 the documents sought must be those that would fall within the definition of standard disclosure, but this does not apply with orders under CPR 31.17 for disclosure against non-parties or someone who is not likely to be a party in the action.
B) In CPR 31.16 the applicant needs to show that the respondent is 'likely to be a party to the action', but for applications under CPR 31.17 this is not necessary.
C) Applications under CPR 31.16 may be made pre-action but applications under CPR 31.17 may not be.
D) In applications under CPR 31.16 the court will sometimes order the respondent to pay the costs of the application whereas in applications under CPR 31.17 the court will never order the non-party to pay the costs of the application