Siberians self-seed around my garden, so I'd expect some seedlings. However, they can take a couple of years to germinate, so you may not see them for a while.

My experience tallies with mad_gal's. Never tried perfume making since I really prefer my floral scents unconcentrated and the blooms in the garden. For some reason I have the idea that iris roots are ground up and used as a stabilizer in perfumes or cosmetics?

Interesting about the uses of Iris root. I never knew this, but apparently you're correct, NHBabs. According to this, it is an ingredient in paint, enamel and mugs:

https://yppedia.puzzlepirates.com/Iris_root

and: In ancient Greece and Rome, Orris Root was largely used in perfumery, and Macedonia, Elis and Corinth were famous for their unguents of Iris.

http://www.botanical.com/botanical/mgmh/i/irises08.html

I'm not much a perfume person, so trying to make my own isn't on my list of things to do, but I do love the scent of the monarda (bee balm) seedheads. I have heard they can be brewed as tea and always meant to try it. (For a while we had vast quantities of chamomile growing wild on the property and I used to cut and dry the plants and combine them with dried mint that grows alongside our brook to make tea.)

My experience also is that Siberian iris spread considerably over the course of years, but whether or not they do this via seeds or root is unknown to me. Maybe both?

IME they spread both ways. The roots expand slowly outward and eventually the center dies out on most of the Siberians I've grown. That is when it is time to divide, but all varieties don't seem to have the same schedule.

I had quite a large clump that was severely reduced when I tried to move them. I collected a few seeds last year and winter sowed them in March (2016). I now have about five plants ready to be potted up. So they are easily winter sowed. They also spread naturally.

No seedlings yet unfortunately. But by golly it's been dry, same as last spring/summer.