The tabs are lost when they are closed out by clicking the X associated with the opened tab.
For this example, we will use "Plates" for our missing tab.
To recover the missing Plates tab, we will simply go to the Windows drop down and select Plates.
The Plates tab will restore after it is selected.
Selecting the desired inventory from the Windows drop down will restore that inventory tab or will go directly to the tab if it is already there.