Prove you're right then.
You don't just have Aston Martins and there be no record of them not being accounted for. The Aston Martin factory or dealership will have records, and being a third party they have a right to have their business with Norton motorcycles or SG depending on who owned them, kept private. They could also have been on loan from the factory like JLR do with their products.
The press are no doubt being gagged by what they could report, this could be at the request of the administrators or other investigating bodies. Part of the administrators job, other than trying to save and sell the company, is to assist and investigate miss-management and past illegal practice, so not all is going to be released.
The press operate in the UK to a higher level proof for the reports they produce than what is expected of the public, any falsehoods, untruths etc can result in serious legal action.
I believe the report said norton motorcycles had Aston Martins, it may not have said specifically who owned them, the company, SG, or the Aston Martin factory. All will become clear in the future.