This week a video emerged on social media purporting to tell "the truth about Traingate" – a strange summer story from last year which focused attention on the country's "ram-packed" train network, and whether or not Jeremy Corbyn was an honest man.

The saga began with a Guardian article about how Corbyn was unable to find a seat on a Virgin train and thus ended up sitting on the floor. It included a video of Corbyn, sitting in a vestibule.

The story gained wide pick-up, and the exact details of the journey became hotly disputed. Had Corbyn been looking merely for a seat for himself – the initial claim – or for his wife too, or for his whole team? On 23 August, the Corbyn team told reporters that it was "nonsense" to suggest that he wanted to sit with his wife. Corbyn himself told another set of reporters this was the case the day after. (It also later emerged that train staff had moved other passengers to first class and he and his team were eventually found seats.)

The story became more complicated when stills and footage released by Virgin Trains appeared to show that there had in fact been empty, unreserved seats available.

The story became even more complicated when the Guardian issued a mea culpa after its initial story was found to have been part-written by a pro-Corbyn activist using a pseudonym.

Now, there is a new twist. An outlet called "Double Down News" has published a video of Corbyn on the train, which has had more than a million views on Facebook. It claims to be "never-before seen footage" from Virgin Trains which it implies shows a conspiracy to smear Corbyn.

Here is the main "revelation": the widely used still image of Corbyn walking through an empty train carriage with free, unreserved seats, that was printed in various newspapers, was misleading. That still was used by some commentators to suggest that there were many available seats, and the Double Down video includes a segment from Nick Ferrari's LBC show in which he points to "10, maybe 12" empty seats without reservations. The Telegraph story at the time refers to "several" empty seats and the Sun described "dozens of rows of empty seats".

Using graphics and a slightly ominous voiceover, the Double Down video shows that many of the unreserved seats were occupied by people not visible in the still. It is evidence that the language about "dozens" of free seats in articles at the time was misleading.

But there's a problem. This is not, in fact, all never-seen-before footage wrenched unwillingly from Virgin Trains. In fact, the key clip (along with other CCTV footage) was made available to news organisations at the time by Virgin. It was broadcast on TV and it was, and is, viewable on websites such as the BBC.

The Double Down footage does not mention this. It also refers to "other images leaked to the press" by Richard Branson. These were in fact put in a press release on Virgin's website – hardly leaking.

Some of the footage in the Double Down News video does appear to be new, and provides extra weight to Corbyn's claim the train was incredibly busy, something neither side has denied. For the most part the video tells a convincing and detailed account of the whole affair.

However, one thing the video doesn't reveal, and which isn't publicised on Double Down's YouTube channel or its Facebook page, is who is behind Double Down. Companies House documents reveal that one of Double Down's directors is Yannis Mendez, the video maker who was being paid by Corbyn's team to film footage on the train, and who pitched the Guardian the article. Mendez insisted that his friend, Anthony Casey, be given a joint byline under a pseudonym. (He was billed as "Charles B Anthony".) This is what the Guardian's readers' editor found most objectionable about the story: a paid partisan activist operating as a journalist, without his affiliation being made clear to readers.

Full disclosure: Liam Young, a political adviser in parliament who has written for the New Statesman, is listed as a co-director of Double Down. An email to Young and a message to the Double Down Facebook page have not received any response at the time of publication. Virgin Trains said it would not comment on the new video.

No one comes out of Traingate looking particularly good. Corbyn's team were initially disorganised in their messaging. The Guardian acknowledges that it made errors in its reporting. And as the Double Down video highlights, much of the wider media should have been more sceptical, rather than following an anti-Corbyn narrative. The saga also didn't look great for Virgin – not just because of a crowded train, but also because Branson's intervention looked like a billionaire meddling in politics.

But for Double Down to present its footage as proof of a conspiracy to smear Corbyn is a little awkward, when it has heavily spun its own story. When calling for less cosiness in the media, it would also help to mention that one of its directors was a key player in the whole affair.

Update: Liam Young has got in touch to say that he resigned as a director of Double Down News at the end of June.