This doesn't sound like an error. It sounds like FMP did what it was designed to do. It's just not what you expected it to do.
When you specify the matching fields option, a powerful but dangerous option, and match on the name field, a row in your xls file with exactly the same name will overwrite all other specified fields with the data from that iimported row. This is what filemaker is designed to do.
In your case, you'll need to set up a more sophisticated import that enables you to append new records when the name is the same but the email address is different.
I'd suggest importing into a separate table and then using a script to analyze each record and correctly update or append the data as fits your needs.
I agree with you. I asked it to match the email field. Import field=existing field. If there was a match, I wanted it to overwrite the fields I specified upon import (with arrows), and if there was NOT a match I wanted it to create a new record.
Turns out it was a data integrity issue (MY error in not better sorting and omitting records with missing data before importing.)
Thanks! User error reigns again.