Consider a situation, when you need to invalidate a patent, and there are already a lot of products in the technology domain (apart from the one under litigation). For example – these can be consumer goods, mobile phones, printing machines, drones or a website, etc. Even those obsolete or current products can act as pretty solid prior art – generally known as ‘System prior-art’.
A System Prior art is different than other non-patent literature as it speaks for its authenticity. Such a reference provides a proof that the claimed technology was in practice before the critical date.
With extensive searching in product catalogs, user manuals, news articles, trade show/exhibition websites, or on YouTube product review videos – the evidence to support the presence of required features can be identified.
If that doesn’t work – we can also do offline research, for example – in books, printed tech magazines, catalogues etc. And even can reach out to people with relevant experience – for example, manufactures, developers, who have seen the entire evolution of the products over the years and may have useful information on the required concept. In fact, people who may have now shifted their career in another domain can also be valuable sources of information, as their experience goes back much further than current tech players!