First, all three of your stamps are shown in the illustrated identifier at the back of each Scott catalog.
To answer your ID question:
A = South Russia, Scott #65, and was only issued imperf
B & C (get asked about all the time) = are from a Latvian set of eight that were intended to be issued under Russian occupation and are noted (not listed) by Scott as not being issued. They come both perf and imperf, and plenty of counterfeits exist. Yours appear to be genuine.