I really try not to bug Mr. Silvera too much, but I did ask about intervals and pointed out the forum here. I know he is busy so I will post his reply:
"About the intervals. Based on the forums, it looks like folks have intervals right for weapons. The intervals for skill-based classes use the same model, but are for skill acquisition rather than weapon training. Here is a hypothetical example. Suppose a Sneak was a class where first level was from 0-3000 xp, and the Sneak gained 30 skill points per level (spread across various skills, although this part doesn't matter). Sneak would have an "interval" of 100 at first level, which means that one skill point is acquired every 100 xp. The basic idea behind the interval system is to enable characters to "feel progress" even after sessions where they don't level up. This also helps balance things relative to spellcasters, who potentially gain a benefit after every xp (i.e., more xp is more spell learning points, which can potentially be directly applied to learn new/better spells). If a player group doesn't like it (e.g., they think the hassle of calculating intervals outweighs any advantage for improving characters "on the fly"), they could easily fall back to a system where all benefits (in particular interval-based skill/weapon training and spell learning points) are acquired at the end of the level."