Hrm. I've narrowed it down to two possible solutions and I've used all the information and neither of my possible answers are accepted. I've double-checked my work several times and can't see my mistake.
Edit: Ah, I see, the bug in the game has already been found several times. Too bad: it'd be a fantastic puzzle if it wasn't broken.
Edit edit: Nope, I'm wrong, found the flaw in my logic, see below.
I think I'm going to sleep on this before I start working my way through all the rot13 text to see if anyone has an answer. Is there a rot13 plugin for Firefox? There must be.
If anyone wants to be generous and check my work, here's the clearest way I can find to write out my chain of logic: what am I missing?
Gur ynfg uvag pbafgenvaf gur cnffpbqr fb gung rvgure nyy qvtvgf ner mreb, be gur sbhegu qvtvg vf avar naq gur svefg guerr qvtvgf fhz gb rvtug.
Edit edit: the above is wrong. This hint says that if there is a unique passcode, it must have this property. That doesn't help you answer the question of whether a particular set of hint answers rules out all the non-unique passcodes which may or may not have that property. Gah. Tricky.
Vs gur frpbaq naq guveq uvagf ner OBGU gehr, guvf nafjref gur svsgu uvag va gur nssvezngvir naq GUNG fcrpvsvrf gur svefg qvtvg, znxvat uvagf bar naq sbhe erqhaqnag. Fb gung'f bhg.
Gur svefg naq sbhegu uvag zhfg obgu or snyfr, fvapr vs rvgure vf gehr gur bgure vf erqhaqnag. Gung nyfb nafjref gur svsgu uvag va gur nssvezngvir, fb abj jr xabj gung pbapyhfviryl.
Abj jr xabj gur nafjref gb guerr uvagf, naq gung gur erznvavat gjb pna'g obgu or gehr. Vs gurl'er obgu snyfr, gura gur fhz-gb-rvtug pbafgenvag cnerf guvatf qbja n YBG, ohg gurer ner fgvyy yvxr guvegl-gjb cbffvovyvgvrf. Fb gurer'f ab havdhr fbyhgvba gurer.
Fb rknpgyl bar bs gur frpbaq naq guveq uvagf zhfg or gehr. Naq gur svefg qvtvg zhfg or na bqq ahzore terngre guna bar.
Vs gur frpbaq uvag vf gehr, gura gur guveq qvtvg pna'g or guerr, naq gur svefg cyhf guveq qvtvgf zhfg or fvk. Gung tvirf hf n fvatyr cbffvovyvgl, svir bar gjb avar.
Vs gur guveq uvag vf gehr, gura gur frpbaq qvtvg pna'g or gjb, naq gur svefg cyhf frpbaq qvtvgf zhfg or svir. Gung nyfb tvirf hf n fvatyr cbffvovyvgl, svir mreb guerr avar.