The Labour leader was travelling on the three-hour 11am Virgin Trains service from London King’s Cross to Newcastle on August 11.
A video emerged last week which showed him sitting on the floor and describing a lack of seats as “a problem that many passengers face every day”.
He then called for public ownership of the railways.
However, Virgin Trains has released CCTV images which appear to show Mr Corbyn and his team walking past both unreserved and reserved seats at 11.07am.
He recorded his video message on the floor around 30 minutes into the journey before finding an unreserved seat at 11.43am with the help of the on board staff, Virgin Trains said.
Mr Corbyn was on his way to debate with Owen Smith in a Labour leadership hustings in Gateshead.
A source in his campaign said they were analysing their own video evidence of the journey and suggested the Virgin footage could have been from a later stage in the journey, when seats had become available.
“Jeremy got on the train at 11am. There were no seats he was able to find and staff couldn’t find any either,” the source said.
Billionaire Richard Branson, who co-owns the train operator with Stagecoach, posted a link to the images on his Twitter account.
A spokesman for Virgin Trains said: “We have to take issue with the idea that Mr Corbyn wasn’t able to be seated on the service, as this clearly wasn’t the case.”
The video of the him on the floor was reportedly shot by freelance filmmaker Yannis Mendez, who was following the Islington North MP during his campaign.
Mr Corbyn, who is filmed reading Private Eye while sat in a corner, said: “This is a problem that many passengers face every day on the trains — commuters and long-distance travellers.
“The reality is there’s not enough trains — we need more of them — and they’re also incredibly expensive.
“Isn’t that a good case for public ownership?”