(a) In the calculation of development impact fees for a particular project, credit shall be given for the present value of any construction of improvements or contribution or dedication of land or money required or accepted by a municipality or county from a developer or his predecessor in title or interest for system improvements of the category for which the development impact fee is being collected. Credits shall not be given for project improvements.

(b) In the event that a developer enters into an agreement with a county or municipality to construct, fund, or contribute system improvements such that the amount of the credit created by such construction, funding, or contribution is in excess of the development impact fees which would otherwise have been paid for the development project, the developer shall be reimbursed for such excess construction, funding, or contribution from development impact fees paid by other development located in the service area which is benefited by such improvements.