How to issue a Purchase Confirmation when there are multiple Export Declarations for air and sea shipments

A domestic company purchased goods and exported them abroad, and now intends to issue a Purchase Confirmation. Since the exported goods were shipped via both air and sea, two separate Export Declarations were generated. I would like to inquire about the following: 1. Should a Purchase Confirmation be issued for each individual Export Declaration (one for air and one for sea)? 2. If goods from multiple suppliers are split between air and sea shipments, should the Purchase Confirmation be issued for the total aggregate amount, or should it be issued according to the amount corresponding to each Export Declaration? 3. Is it acceptable if multiple suppliers' goods are combined within a single Export Declaration?