I don't read the term "dual opposed heads" as 4 heads at all. I read it as two heads on opposite sides, which I believe is how the Twiggy drive operated and the reason it had two cutouts on opposite sides of the disk from each other. So I would propose it is a matter of semantic inference.

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Yes -- thanks, Mac128, for correctly interpreting what I wrote, despite my unintended efforts at obfuscation.

Those drives were certainly odd-looking, as were the floppies they used. I had a chance to buy a box of broken Twiggy drives back in the late 1980s. In a rare moment of self-restraint, I passed up the opportunity. Whenever I see how much these things sell for on eBay, I kick myself.