When FIFA needs a file to be used in the game it searches in the following order

1st in zdata_XX.big archive

2nd in the data subfolder

If the same file appears in more zdata files, it is used the file archived in the zdata with the higher number.

When FIFA needs a file to be used for its GUI it searches in the following order

1st in the data\gui subfolders

2nd in a big archive present in the data\gui subfolder