One more wrinkle ... the decree just says the non custodial parent claims the exemption in the odd years... it is possible that the custody (according to the IRS rules) could change every tax year depending on where the child lived during the year. If this happens then it is possible that the same person would legally claim the child every year.
For instance :
2018 MOM claims as custodial parent
2019 MOM claims as NON custodial parent
2020 MOM claims as custodial parent
2021 MOM claims as NON custodial parent
