Every time you teir up or win credits in ths game you increase your (reported) Career Earnings. When they gave you the credits that's when you see them on your Credit report.
For Example: you entered a C.C. event that offered the prize credits for the top 10 finishers, when they receive the credits their 'Career Earnings' will increase or there was another example: Recently ther was an individual that won a free trip to an up coming event, his 'Career Earnings' sky rocketed. In most cases when you see 'Career Earning' increased the indivual has already spent them(credits).
However, there are some that play well enough to be in a constance earning mode. Just like in the PGA in RL you don't have to be the winner of all or any of the tournements you just need to finish somewhere near the top to enjoy the benefits of 'Career Earnings'