This [Act] determines the priority of conflicting claims to collateral. However, if the relative priorities of the claims were established before this [Act] takes effect, [former Article 9] determines priority.
(b) [Priority if security interest becomes enforceable under Section 9-203.]
For purposes of Section 9-322(a), the priority of a security interest that becomes enforceable under Section 9-203 of this [Act] dates from the time this [Act] takes effect if the security interest is perfected under this [Act] by the filing of a financing statement before this [Act] takes effect which would not have been effective to perfect the security interest under [former Article 9]. This subsection does not apply to conflicting security interests each of which is perfected by the filing of such a financing statement.