I hope this question makes sense. Thanks in advance for any help.
Let me try to explain overdelivery credit with an example.
Assume that you have set your daily budget to $10 per day. Obviously you are expecting to spend around $300 a month. The software that controls your daily ad spend may sometimes show your advertisement even after you cross $10 per day (the software is probably not perfect).
Because of this, you may collect clicks equivalent to, say, $400 in a month. Anything over 20% of your budget for the billing period is credited back to you as overdelivery credit.
In the above example, your overdelivery credit will approximately be equal to -
[400 - (300 x 20/100)] = $40
In other words, you are basically getting free traffic for $40 (overdelivery credit amount).
Is it just a way for Google to point out that an individual could be recieving many more clicks?
Well... Not really.. its just that Google AdWords program overpeformed on that ocassion and they don't want you to overshoot your budget.