I'm on a breeders site and they are advertising that this pair of conure's gender was determined surgically. I am familiar with the DNA method but have not heard of a surgical procedure. Seams kind of excessive.
Seams disgustingly excessive to me, though it is a very minor surgery.
I don't know the prices but I suspect it used to be cheaper than DNA. Molecular methods though have progressed at such speeds that a DNA test can now be very fast and affordable.
Perhaps his were sexed some time ago when the surgical method was more practical.