Starting strength wiki refers to these strength standard tables.
Are the values listed there the upper limit for the category, or the lower limit?
In other words, I'm 81Kg and I'm able to squat 90Kg, am I 'untrained' or 'novice'?
You're getting close to "novice" level, it's not a low/high limit. If you squat 100 kg weighing 82 kg you are a novice according to the chart. But it's completely subjective of course.