Speed: Last I heard, said 1900Cs went to the Frontier certificate during the formation of Era Alaska. The only Era 1900 based in the bush (to my recollection and about a year ago) was in Nome. This 1900 was flown by Frontier pilots doing pax service from Nome to Gamble and Savoonga. The only "big" metal I can think of on the HAG cert are the Shorts from Arctic Circle Air - and those may have very well gone to Frontier as well.
I do know that at one point HoTH wanted to consolidate the four certificates into two, not sure how that has progressed.