SC,
The standard solution for this type of requirement is Product Allocation.
Product Allocation - Availability Check and Requirements in Sales and Distribution Pr - SAP Library
You can configure Product allocation such that during Sales Order entry/change, the maximum quantity of confirmations are limited; according to specific characteristics in the Sales orders that you configure (such as customer). These confirmation limits are defined by date.
Meanwhile, I realized GATP (Global Availability To Promise) might be a solution. Have you ever heard about it?
Yes I have heard about it. GATP has its own Product Allocation solution, which has more features than ECC Product Allocation. In addition, GATP permits combining Product Allocation with availability checking methods that do not exist in ECC.
Best Regards,
DB49