English to German Law/Patents Law: Contract(s)

I'm translating, from English into Polish, a non-disclosure agreement that was (most probably) originally translated from German into English. Here's the context:

''The above obligations shall not apply to
a) Confidential Information known to a Party prior to the date hereof and not obtained or derived from the other Party nor from a third party which is under a secrecy obligation to one or both Parties;
b) Confidential Information known or available to the general public prior to the date hereof, or Confidential Information which becomes public or available to the general public after the date hereof through no fault of either of the Parties;
....
The burden of proof for any exception as listed above shall rest with the Party alleging such exception.''

I am not entirely clear about the phrase ''allege an exception''. Does ''alleging'' in this context really mean ''making an exception'' or ''invoking/relying on an exception''?
Any help would be greatly appreciated.