What was new in this week's revelations was the detail of how the donation came to be made.
Those details were provided to the NZ Herald by Jami-Lee Ross as part of his effort to expose National's donations practices – practices he was once heavily involved in himself and now criticises.
It included the role of former Trade Minister Todd McClay, who asked Ross to contact Lang's office to arrange the donation.
National MP Todd McClay, the former Trade Minister helped arrange a donation for National. Photo / Ben Fraser
National Party leader Simon Bridges used the defence which parties in such situations always fall to: that the donation was within the law.
Prime Minister Jacinda Ardern also conceded it was lawful but added that she believed it was "outside the spirit of the law".
That law prohibits donations from foreigners of more than $1500 and was a bid to guard against foreign influence.
A year later in 2017 the National Party returned two donations because they were from overseas donors – one was a $4000 donation from a Zhang Xinyuan and the other was $49,975 from an Australian company, Go-Airlie.
National kept $1500 of the Zhang donation but returned the full $49,975 of the Australian donation.
So that rule may be working as intended, but there has been increasing attention on the ability for someone to donate if they have a New Zealand registered company.
That is being considered by the Justice and Electoral Select Committee and in the corner of reform are the intelligence agencies, wary of foreign influence.
Details of how Lang's donation was organised provided an interesting glimpse into a process parties normally like to keep a bit hush-hush: the process of handling a donation.
The reason they like to keep it quiet is because of the potential for embarrassment.
Donations have long caused headaches for political parties as rivals and media move to question the probity of them.
NZ First has gone through donations scandals, Labour has too.
Over the years, National in particular has been questioned over donations, not least because it tends to get more of them.
There was its use of the now defunct Waitemata Trust before 2005 to channel anonymous donations through without revealing their source.
That trust was disbanded after the Electoral Finance Act, which set in place tighter disclosure rules.
The law was repealed by National in 2009 but the donations disclosure rules were kept on.
Disclosure brought its own problems for political parties and donors.
Putting big donors in the public eye made it easier for political rivals to take pot shots at motives, alleged conflicts of interest and fundraising practises, from dinners with ministers to more intimate events.
In 2014, Key was criticised for a private dinner with businessman Donghua Liu who then donated $25,000 to Jami-Lee Ross.
Ross returned the money later – at the time Liu was facing domestic abuse charges which were later dropped. Liu has also donated to the Māori Party and Labour.
More recently was a $100,000 donation organised by Chinese businessman Zhang Yikun, which the Serious Fraud Office is looking into after Ross brought it to light.
National has insisted it handled that appropriately as a collection of smaller donations which did not exceed the disclosure threshold.
But for every donation that prompts outrage, there are plenty that pass unmentioned.
Changing the rules can be fraught unless there is consensus, as Labour found out when it pushed through the Electoral Finance Act in 2005.
One-sided reforms are easily seen as an attempt to protect one's own funding sources while drying up a rival's.
Labour would not want a change that would restrict the trade unions donating any more than National would want companies restricted.
That is why Justice Minister Andrew Little has been happy to leave it to the select committee, although he has now suggested that if that takes too long he may do something off his own bat.
There have been calls for donations to be capped, for disclosure limits to be lowered, and for public funding of parties to be introduced to reduce the reliance on donations.
No political party can afford to be too picky.
All sides are afflicted with that disease of self-interest.
