(A) All agencies and departments of the village shall file with the purchasing agent detailed estimates of their requirements in supplies, materials, equipment and contractual services in such manner, at such times and for such future periods as the Village President shall prescribe.
(B) The requirement for preparing estimates shall not prohibit any agency or department from filing with the purchasing agent at any time a requisition for any supplies, materials, equipment or contractual services the need for which was not foreseen when the detailed estimates were filed.