When doing a dataload and bring your CSV files into the system, it is always a great idea to setup a custom field or two to capture the information which we don't have fields for IE
We capture standard information (First Name, Last Name, Address, etc) but not special information which is key to your business IE Price of season tickets, how many employees, what their favorite colour is, etc
But what happens when the data isn't loaded in?
In cases where the data isn't loaded in, it is normally because the data doesn't match what is in the system IE
If you are loading in a value such as £15 and your spreadsheet/CSV says £15 - logic would say they match.... But, check the formatting as one thing Excel will do if you set the field to be currency format, it will leave the value as 15 but when you look at it, it will be £15. Causing the data not to be loaded in.
Check the formatting before loading