Display the data processing workflow and its progress in a table format. Additionally, display any errors encountered during processing, for example, instances where a student is missing from either Excel A or Excel B, or where marks cannot be located.

Incorporate a button that loads dummy data for both Excel A and Excel B to facilitate testing purposes.

Enable users to upload two Excel files: Excel A (the "tailor-made mark sheet") and Excel B (the "official mark sheet"). The system should transfer marks from Excel A into Excel B by matching student numbers, then allow the user to download the updated file as Excel C.