No, they dont inform in case of incomplete application/missing documents. They just return the application back. In some cases they are lenient with missing documents if they are not mandatory and are generally kind of supporting documents. If Signatures, Forms or any mandatory documents are missed expect it to be returned back. However, once you receive an Acknowledge of receipt (AOR) you will be informed about all the future updates. They will only start Sponsor Eligibility if your application is accepted so in this case you will informed.