It's the paralegal/law clerk's job to interview, get the backstory, find the details like that. You don't pay a lawyer hundreds of dollars an hour to put together a summary of what happened.
If Nikki had even gotten to speak to him at all (which seems unlikely given the pressure GLK/H was apparently put under by Daddy), she likely wouldn't have known to ask about the fuel anyway. He clearly didn't realize he'd made a mistake in using that instead of whatever Luke instructed, so it never came up.