df.units.xml:skill_rating seems to have changed prior to 0.47.01

[PatrikLundell]

Looking at a 0.44.12 save (both in 0.44.12 and 0.47.03, with no difference), I find the highest skill_rating value being 54, with most values below that being present, indicating the scale might be open-ended. In addition to that, the XP thresholds may have been adjusted as well, given that a randomly selected skill (Mason) with a value of 26 is listed at 1196 XP, corresponding to Talented according to the XML. Competent (3) = 444 XP, Skilled (4) = 824 XP.
No. There is only a weak correlation between the skill rating and experience value on units (skill level 16 has at least one unit with 0 experience, for instance), so I don't think you can look at units to draw any conclusions.

Needs further investigation.

[lethosor]

I wasn't able to find any unexpectedly-high unit.status.current_soul.skills[X].experience values in a fresh 0.47.04 save. The rating values have been unbounded for some time, I think, and I'm not sure what the experience cutoffs above Legendary5 are.

Actually, if you were looking at the xp_threshold attribute of skill_rating, that's the experience needed beyond the current level to get to the next level - e.g. once you're Skilled, you need 900 more XP to become Proficient. My logic might be off by one or so, but here is a possibly-relevant place in manipulator where this is displayed - you'll probably be able to find e.g. "Skilled (400/900)" dwarves.