You can check your Incentive history by logging into the website and clicking on Incentive History. Your referred people will be listed there.
If they are not in your list they, most likely, have not used your referral link or they have navigated away from your referral link page.
We are not able to give any details about other members, so if you are certain that something has gone wrong with the referral process you will need to get your referrals to email email@example.com and ask to have their account linked to their referrer.
They will need to include your referral link and the email should be from their registered account.