The possibility of copyright problems was raised at least twice when National was putting together its 2014 election advertising.
The battle over whether an unlicenced version of Eminem's Lose Yourself was used for the political ad is in its fifth day at the High Court in Wellington.
Ad director Glenn Jameson said they originally used Lose Yourself for test ads.
But the plan was always to replace the track with a "sound-alike" before it went to air.
"Lose Yourself had a steady syncopated beat. It was an example that came to mind as something I could use to prompt [a staff member] to find me that type of beat for a track," Jameson said.
"I can say to people 'go and find something like that'.
"But obviously none of it ends up in the final product.
"My voice wasn't used after the test, none of the pictures were used, by the end it's all original material."
After going through testing, and a final version being put together, the ad was presented to campaign staff.
They questioned if the backing track was too similar to Eminem's work.
"They raised problems with being associated with Eminem, or [legal] use of the track."
Jameson was asked to put together alternatives, and two new versions were created.
But when he played the original and alternative versions to National Party campaign staff, they said they preferred Eminem Esque, as long as they could use it.
He told them the licensing system meant they could use it.
"If Apra approved the track, and licenced its use, then it would presumably be fine for the National Party to use it.
"I said it looked like we would be able to use the track, but we would need to double and triple check the legalities."
It was only in late August 2014 when the ads had started to air and they received inquiries about the use of the track, that new music was "urgently" sought.
Barrister for the copyright holders, Garry Williams, questioned the evidence Jameson gave.
"So you were all 'pretty relaxed' about [using the track], but immediately after a meeting you were instructed to go and check the legalities?
"That sounds a little inconsistent."
But Jameson was insistent that they never saw any major red flags.
"We wanted to make sure everything was ethical and above board," Jameson said.
"It was in the public domain and had a licence, that's how we buy tracks.
"We go to Apra because we pay them huge fees and they're supposed to protect us. We thought we were safe; it's not as if we were trying to be dodgy about it.
"I've never had problems with it in my 30-year career, this is very unusual to say the least."
National Party secretary Greg Hamilton said the party simply trusted that judgement, never expecting there to be a problem with copyright infringment.
He said even though there was a record of questions being raised, it was never a serious concern.
"It wasn't people, it was a person, one staff member who raised it," Hamilton said.
"Our approach was that we had experts, professionals who did this as their bread and butter.
"Our approach was send them away and make sure this is all okay."
Barrister Garry Williams questioned if they really had expert advice, as none of them were lawyers or copyright specialists.
But Hamilton said they'd trusted the qualifications of their team.
"When you have confidence in those suppliers, and they've been specifically asked to reassure us to check this is 100 percent correct.
"After receiving those assurances, I just had no cause to think that there was a problem with the licence."
The hearing is set down for six days.