LR Classic v8.2.1 stacking missing from context menu

You can stack photos in a collection -- I wish the rules for stacking were that simple.  Here are the rules I know of:

- If you stack photos in a folder, you can see that stack in parent folders and in All Photographs, but not in collections or smart collections.

- You can't stack photos from different folders, or from folders and collections together.

- You can stack photos in a collection, but you can't see that stack in the parent collection set, in folders, in All Photographs, or smart collections.

- You can't stack photos displayed in a smart collection.

- You can stack photos in Previous Import, but not in Quick Collection (though it's called a "collection") or All Synced Photographs.

- If you create a virtual copy while in a collection, the copy will be stacked with the photo in its folder, not in the collection, and the stacking won't be visible when  viewing the collection.

- In contrast to creating virtual copies, Auto Stack By Capture Time creates the stacks in the folder (if you're in a folder) or the collection (if you're in the collection).

- If you edit a photo externally with the option Stack With Original, the edited photo will be stacked in the containing folder regardless of which source you're viewing. If you edit a photo while viewing a collection, two stacks will be created, one in the folder and one in the collection.

- When you create a Capture Frame from a video, Lightroom stacks the capture frame with the video clip. The stack is only visible when viewing All Photographs or the folder containing the clip. If you captured the frame while in a collection, the frame will be added to the collection but the stack will only be visible when in All Photographs or the containing folder.

- When you select the options to re-import exported photos with the Add To Stack Option, the stacks will be created in the photo's containing folder and only visible there, even if you are exporting photos from a collection.

(And no, I can't keep these in my head. I helped Adobe correct the manual two years ago: Lightroom: Incorrect documentation for stacking | Photoshop Family Customer Community)