It took two more synchs and a lot of deleting, but I cleared out the extra records. Thanks for the instructions.
That said, although I'm successfully back to Square One, I still can't get the modified records to import and update the existing records.
If I select "Update existing records by matching key field(s)", then Method automatically selects RecordID as the key field. That makes sense, as it appears to be a unique identifier.
If I select "Do Not Import" for Record ID and attempt to Import, then I get the error:
ERROR: One of the columns you've selected in where
statement was 'RecordID' which was not added in step
'Prepare Data' of importing. Please add the specified column
and continue.
If I select "To Existing Field" and match up to RecordID and then attempt to import, I get this error:
You attempted to update values in the field "RecordID" which does not support edit. All columns except for 'RecordID' column were updated.
...which might sound encouraging, except that the next screen is a list of all 50 records, displaying the error:
Error:Failure. The Table does not support edit.
How do I configure this import correctly so that the records are updated with new data?