Are you completely sure it wasn't a seasonal shed or something else? Also, I don't think it is the serum DHT that matters when it comes to hair loss, but rather the Type II DHT. The further reduction of serum DHT that you got on dutasteride is probably due to the Type 1 DHT that is being blocked.
I wonder if your shedded hair would have returned if you stayed on finasteride or gave it more time. However, it is good to know that you can always switch to dutasteride if you don't think finasteride is providing good results anymore.
Haven't check the forums in a while. Well Finasteride was only providing approx 70% type 2 reduction, yes this is essentially the only kind that matters as it is synthesized in the dermal pappila and acts as an autocrine hormone. Dutasteride is 3x as potent at inhibiting type 2 so usually the larger reduction is from type 2. I remember reading that finasteride at its best reduces type 2 by about 85-90%, however it you can fall anyhwere between 60-90% on that curve. Dutasteride inhibits 98-99% of type in in just about everyone. In my opinion this is why its so effective. Been about 7 months now and im still counting 0 hairs in the sink and shower. Its crazy how unnaturally good this drug is for some at stopping hairloss.