I have an identical yellow Super Sport (as well as a matching men's) as the OP's. They were donations from a college friend with the understanding that any proceeds from their sale will go towards our charity Ukraine Bicycle Project. We make fillet brazed frames on a college campus outside of Kyiv and then build them into transportation bicycles for pastors in the eastern war zone where only military vehicles as allowed on the roads. The seat tube on the SS I'm responsible for now is also bent just like hers. This characteristic of a tube bending when other tubes are fillet brazed to it is common. You can see this often on the head tubes of fillet brazed tandems. Most people just don't notice.
I've taught framebuilding classes on a regular basis for 45 years. Usually students make lugged frames in class but sometimes they will do a fillet brazed one. Here is a picture of an example a student made so you guys can see what they look like in the raw. This is the top of the seat tube. Of course in this case the fillets have been filed. Some builders like Tom Ritchey or Normal Taylor (the brother that actually fillet brazed Jack Taylor frames that I personally saw make frames when I was apprenticing in England) can flow the brass so it needs little or no after brazing touch up.
