All the court orders would have to be reviewed to see the provisions of the orders.
If the only provision on tax exemption is "does not apply", this likely means that the court made no decision on the issue of tax exemption.
Under IRS rules, the parent with whom the child spends most of the time is the parent entitled to claim the child as a dependent. Since there is no court order that orders the custodial parent to sign the exemption waiver to the noncustodial parent, the custodial parent does not have to allow the noncustodial to claim the child as a dependent.
The order of child support can be reviewed by the court when one of the statutory provisions exists. Depending on how long ago the last order was entered and other facts, you may be able to ask the court to review the order of child support, including the provision on tax exemption.
You can review the facts with an attorney to see what options are available to you.
What does the child support order say? If neither the decree, nor the child support order indicate the exemptions, then you would need to go back to court to clarify the order, unless the parties agree.