Book 3, page 128 - there is option to ask merchant about Ragadorn, to ensure that he isn't just pretending to be merchant from there. It should be available, if You have ever been to Ragadorn.
In book 3, Drinking potion, that should restore 6 endurance points (in possession from book 2), doesn't result in any endurance gain
On page 301 (third book), there is option to make use of hunt skill, to silently approach guards and poison them. unfortunately, despite having hunt skill, I can't choose this option.
After killing undead tentacle monster in main chamber of ice fortress (book 3, the monster with 50 endurance), lone wolf splits error: