Or is that implied by '1' combined with the absence of any other bits?
Yes.
is it guaranteed that there are no other cases that generate a result of just '1'?
Yes.
I think the help file could be a little bit more clear about this
Looking at the help file, the errors seem fairly self-explanatory except for "bad script" and "bad server". In retrospect, I probably should not have added these as errors because they can only be returned if an event id is specified that does not have the original server/script present, so they should have been subsumed under "bad id". As they are already there, they will require a more complicated explanation in the help file.
