Is name, rank and serial number really something only given by POW in movies?

Basically a guess - hence “assume”. I await clarification by those in the know.

Because the Russian empire AFAIK was heavily connected with the German states back in the day, and so likely adopted their legal system, or a variant of it - more based on an inquisitorial process by an authoritarian government; which would describe the Russian empire governance better than “British Parliamentary democracy”. More likely than that it would have adopted a system from Britain, where the defendant is given a large number of rights, the judiciary is independent, and the system is more adversarial. (Knowing the history of Lenin and Stalin, the idea of changing the system to give more rights to prisoners probably was not their priority.)

Riiiiight. That a free confession made by a 21 year old in a Court controlled by his enemies.

this is evidenced in my source for everything concerning the treatment of POW’s: The Great Escape. Steve McQueen completes his famous motorcycle jump (while wearing a stolen German uniform) but soon crashes and is captured. While surrendering he flips his lapel over to show some piece of identification.