I always got the impression that the SW was a Raleigh thing only.
I've got a 1957 Schwinn Deluxe Racer that belonged to a family friend since new that has an AW hub, as far as I know, the bike has never been touched.
I don't recall ever having an AW marked 1957 though, but I have had 56, 58, and 59 AW hubs in the past, but those were likely all 36h off of American bikes.
As to adding springs to the SW, I've run across a few with the flat spring modification done, all were working but had significant wear to the tips of the dogs. Unless I was doing a museum type restoration for historic purposes or display, I would not use an SW hub. They are finicky at best even when their working right. They don't shift well, they don't last, and can't take any abuse, and cold weather is their enemy. The engineers really dropped the ball on the SW, and they knew it and gave up on it. I've sold a few over the years on eBay, they always sell and collectors grab them up but I would think they were for display more than to use. About 16 years ago I did a clean out up in NY and came away with about 8 SW hubs that looked brand new but without packaging. My guess was that the shop removed them day one and stuck them on the shelf. There were another 15 or 20 of them that were stripped for parts. I sold every last one of them on eBay. I think I may still have a few used one's laying around but not intentionally.