Create a form which can be used in Wordpress, but is not dependant on Wordpress, which makes a call to an Airtable API first to validate against existing data, then to add to fields if the validation is successful.
Example: User fills in form, form first checks with Airtable API to be sure the data from field A exists on the table, if data from Field A exists it then checks if the data has expired by using another field inside Airtable. If the data from Field A doesn't exist, or if the expiration date has passed, the user should see an error message explaining why their form could not be processed and offering them a chance to try again.
If the data from Field A is valid, and the expiration date has not passed, the form should be submitted and the data should be saved to a table. The form fields should also be sent to the Airtable via API.