If the person doesn't submit a reply to your feedback, it still counts for your overall trade rep.
The reason you may have a lower number than you're actual total is because you traded with the same person more than once. If you trade with somebody and they give you more than one itrader, only one will count towards you total. So in a way, the number displayed by your name is the total number of people you have traded with. Your total itrader number is located on your itrader page.