Sheds are really hard to say anything about. First of all it isn't exactly clear what the mechanism of a shed is. Secondly you need to be able to distinguish between your regular male pattern baldness shedding and finasteride shedding and that can be difficult.
That said, personally I would say that a shed (which is from finasteride) is a sign that it's working. But you can easily find people in here who claim that they have never recovered from their sheds. But that's probably the reason they are here.