The best error free binding relation is the absolute filepath, so one csv line relates to one file, given by the value of the system pseudo tag-field "%_path%" on export and on import selected by the placeholder "%_path%".
The "%_path%" item can reside at any position in the csv line.
I use to put it at the very end of the csv line.
See also ...
Import tags from text file
DD.20120909.1925.CEST