Earlier quoted context omitted.
Few people can believe that there are as many as 386,356,909,593 games on the tiny 2x2 board. Needless to say, nothing is pruned there either. A game could visit as many as 48 of the legal positions and have dozens of passes (but only 2 consecutive ones, which ends the game).
Well it "ends" the game but play can resume. Plus, there's the crazy hypothetical play in the way-over-complicated Japanese rules. I think, in theory, you can play multiple almost-compete games after the game is "over". Each hypothetical play is just to resolve one group, as I understand.
That's why our paper "Combinatorics of Go" assumes the so-called Logical Rules at http://tromp.github.io/go.html, which do end a game on consecutive passes.