The tab geometry suggests they are lanced and formed from a flat strip in one hit of a press.
The quantity in which they are normally used suggests that the remainder of the forming, e.g. rolling the lanced rectangle into a circle, should be fully automated, but that's a tall order.
One way is to curl the strip in the same (progressive) die as the lance and form operation. Normally the last station in a progressive die cuts off the finished workpiece from what started as coiled strip. But closing (or nearly closing) the circle makes that very difficult, unless the product blank is crosswise to the strip, but then the shearing operation would leave a burr and possibly some distortion on the circular edges.
So, maybe the strips are lanced and formed and cut off in a relatively simple die in a relatively small press, and the remainder of the operation is done 'by hand', e.g. with skilled labor inserting the blanks into other presses that, e.g. curl one end, then curl the other, then squeeze the ends together and curl the center.
All of that is speculation based just on observing a few photographs of the finished product; it could as well be made by elves.
