Check forms for missing details, return them for correction. Every one is ready to run, and you can adjust it in plain language.
Mark spreadsheet rows needing correction before import.
Your reporting table gets valid new spreadsheet rows every 15 minutes, with import counts and row-specific fixes waiting in the sheet.
Add valid email submissions to the table and reply with their IDs.
Turn emailed entry requests into database rows, with a reply that confirms the ID or tells the sender what to fix.