What are the best practices for creating profiles when there are invalid mappings?

Summary: When we run a data load and have invalid mappings, we download the invalid mapping account IDs and then send an Excel spreadsheet for the profile data to our business clients for them to complete. This Excel spreadsheet contains all of the profile fields they need to complete for these new account IDs. Once they complete the spreadsheet, they send it back and we import the file to create the new profiles.

How do other businesses go about their invalid mappings process? Just looking for best practices from other businesses on how they manage this process.