You are assuming the BTC are still in the account of the person who "owned" the address. And the internal ID would just show that a deposit came into the said address and that the proper user account was credited with the BTC. None of that will have any of your information in it.
Correct, I am assuming that once the money is inside MtGox they log all the internal transaction with BTC addresses. I know they log them because I have account history. I assume they are associated with BTC txn data because I can't see it working otherwise.
And it could be that they are logged somehow that the support team can't access or know how to access. Similarly, if you were to call Bank of America or Chase up, and had an issue with your account, you can't just talk to the support people. There are account research specialists whose sole job it is to research issues like these! But once again, we are making assumptions about a system we know nothing (or close to nothing) about.