I know that Orion behaves like that. If the window is not open, it will not show up in the window switcher. We are on the same page.
I open a SAVED tab group, lets call it "Tab Group A." When I go to move a tab from my unsaved, general browsing tab group into Tab Group A from the menu, it only shows up as "X amount of tabs".
The above picture is my saved tab group that is clearly open.
This other picture is the general browsing window, trying to move a tab into NL2DS as shown above, and its referred to as the number of tabs in the window, which at the current moment is 3.