There have been a few times I unsuccessfully tried to add a domain name to my parking account, and because the domain name was already listed in another account, it didn’t get added to mine. When you are adding names to your account, be sure that they are all added.
Let’s say that I put a domain name up for auction. I’ve been parking the name with Internet Traffic for a year, and I don’t remember to take it down before the auction (or don’t wish to take it down in the event it doesn’t sell). If and when you win the auction and try to add it to your account, it won’t let you if it’s still in my account.
If you don’t see an error message or email from the parking company to notify you of a conflict, you’ll see that the domain name is parked with that provider, but the revenue will go to the former owner. Sometimes domain owners who have a lot of names will never even notice this, so it’s on the new domain owner to be sure the name was added.
For some companies, it is very obvious when the domain name is not added to the account. I also believe some companies have a notification process that automatically creates a ticket if there is a conflict in the system. Your ownership should be easy enough to prove with a Whois search, but the real issue is if you don’t notice that there is a conflict and it’s not reported automatically.
After adding new names to your account, you should always be sure to check the confirmation email from your parking company to ensure the domain names you want added were properly added. You should also monitor your daily traffic and revenue reports to be sure that they are accurate.