If you title your section “Clients” and the brands are no longer working with you, this would be somewhat misleading. If I were to write an article about you or base my buying decision on the list of customers, this would not be a valid strategy and would lead to a misalignment between the presented information and what the actual case is.
On the other hand, if your portfolio states “Brands who have worked with/used X”, I would expect that some of those may no longer be existing customers of yours but have still decided to give it a shot and spent some time using it.
It’s not uncommon for some small SaaS solutions to list Facebook, Twitter, Instagram, or other popular solutions as users of their applications. Most of the time, their own customers link to their application or embed it in some form which is completely different from the actual company purchasing a software and utilizing it in their branding efforts.
This type of section may be labeled as “Our users” or “Featured at” or something else misrepresenting the actual list of clients.
There is one exception to the rule which includes case studies of former clients. Whenever you publish formal case studies with the participation of your customers (their quotes, reviews, etc.), that’s still valid feedback that cannot be erased lightly and may bring value to prospects.
A couple of months back, I was researching a new opt-in solution for some of our websites. I stumbled upon a popular vendor used by many—they’ve listed reviews from “customers” and have added their logos to their list of clients.
Since I wanted to see how those opt-ins work in practice for some of the brands that I follow myself, I did a brief research browsing their websites and looking for opt-in forms embedded from the vendor’s platform. There were 4 out of 5 who were no longer customers and switched to other solutions.
I took a note and signed up for another alternative that is nowadays used more frequently simply because I failed to see practical use cases from the marketed brand and found other promising solutions while browsing their portfolio.