I hadn't tried this until you said. I then went there and did it, and found out that If I log in from the 3rd device and click in "Add", it only shows Kaspersky VPN and Kaskersky Password manager, like in this image:
Then if I use the Kaspersky executable that I installed on the previous machines on the 3rd one (because it already comes with the license), what I see when I launch kaspersky on the 3rd machine is this, a message saying "You don't have an active subscription in [my email]":
And then on the dashboard the 3rd device shows up under the tab devices (but not under the Subscriptions tab I showed before), but it shows up like this:
As you can see, Kaspersky is really confident I am using the 3 devices I paid for, although I'm only using the subscription on 2 devices