back when I first learned about them - back in 1970 - they didn't.
The wikipedia article you are presumably relying on does talk about "T-shaped sections" for specialised applications, but doesn't suggest that this is what is usually meant.
I make a habit of it. You didn't post the link you seem to have been relying on, and and you don't seem to have learned as much from it as you might have done. Your claim that the metalisation can be an aluminium/zinc composite strikes me a dubious. The metalisation can be either aluminium or zinc, but putting both down on the same film does seem to be improbable. Metal-spraying the ends of a capacitor with finely divided molten zinc to connect the aluminium films to real wires does seem to happen.
The self-healing properties of evaporated metallic films does imply the films are made as thin as they can be - which is to say just thick enough that the thinnest areas are just one atom thick. I should ahve thought of earlier - I've known about self-healing forever, but don't get to think about it all that often.