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It shouldn't technically be there. If you really want it off, I'd talk to NFCU and get the address to their credit reporting team (or use the address for them on your credit report) and send a dispute there first. Then try with the bureaus.
In all seriousness, I'd maybe even leave it haha. It's helping with your credit mix part of the score anyways. And the AAoA hit will wear off soon enough.
I'm also not an expert on disputes, maybe someone who is can chime in soon.
Definitely sounds wrong. I'd start with NFCU (phone and their address on your credit report). If that fails, you could try disputing directly with the credit bureaus. I think the key word you want to use here in disputes, etc... is that the loan was only preapproved, never disbursed.