Each game fork has its own rules. Additional forks may be possible if the particular game would allow it at the time. Reunifications must be legal in all affected forks.
...and of course bear in mind that this game was actually played the first time in special conditions in 1953. It is now being spooled out with the moves in reverse order for your amusement. The reason for the current seeming long gap is that at this stage in 1953 the original Dr Heinz Tuj died of syphalis when it was his turn. The others therefore used transcripts of what he had said previously to piece together a final (or initial, as it is being reproduced backwards) move for him. Now read on.