Does Setting Validation In A Query Possible?

I'm making a database with 50 fields for the shops of my company. Among these fields, the data of 20 fields must be submitted to us (head office). The data of the remaining 30 fields (like customer address) is just for generating receipts.

At the begining, I set the validation rule of that 20 fields to be "Is not null" in the Form. If the required data (20 fields) is not entered, messages will appear and the record cannot be saved. Then I use the Query function to extract that 20 fields. However, our staff said they might not be able to obtain the information of the 20 fields in the first time. The customers may send them the info later on. So, it not good for me to set any validation rule in the Form.

I would like to ask how I can ensure they submit the data of the 20 fields if I release all the restrictions in the Form? Could I set any validation in the Query so that error message will appear if not all the required fields are filled?

Thank you.