Let's begin by reviewing some best practices that will save you a lot of time and frustration when performing your imports.
Best practices
Internal IDs
My first recommendation may sound inane and irrelevant; however, I suggest the first thing you do is go to Home icon | Set Preferences and check the SHOW INTERNAL IDS checkbox:
Set Preferences
The easiest way to add or update data is to use the internal ID for a record. Incidentally, you can see the internal ID of each record by looking at the URL of that record. It is easier to reference the ID than it is to reference the name of the record because you can't make spelling mistakes when referencing an ID. A name, on the other hand, can be misspelled or contain slight...