(1) If the determination of the question whether evidence adduced by a party is relevant depends on the court making another finding (including a finding that the evidence is what the party claims it to be), the court may find that the evidence is relevant:
(a) if it is reasonably open to make that finding; or
(b) subject to further evidence being admitted at a later stage of the proceeding that will make it reasonably open to make that finding.
(2) Without limiting subsection (1), if the relevance of evidence of an act done by a person depends on the court making a finding that the person and one or more other persons had, or were acting in furtherance of, a common purpose (whether to effect an unlawful conspiracy or otherwise), the court may use the evidence itself in determining whether the common purpose existed.