Paul, you can either just ignore the fields you do not want similar to 17, 20 & 23.
Or you can just name the fields that you want update providing Access recognises them OK.
I know this is a VBA forum but you should be able do this without VBA.
You can
1. Import the backup table
2. Run an Update Query to update the missing data.
3. If the update is successful delete the imported table.
I would import the table anyway to manipulate it with VBA as you can do all the work in Access.