Padded Jack gives AC 2, or AC 1 if worn under munition or half plate. It has a 1 stone encumbrance.
A Restricted Armor selection is "hide or lighter".
Is "lighter" a reference to the encumbrance of the armor, or the armor class - would Padded count as Hide or Lighter, or should it be treated as Leather (Narrow Armor)?
Same goes for Half-Plate, AC 4/3Stone, and Three Quarters Plate - AC 6 for 4 stone - Chain is AC4/4 stone. That's a bit more of a stretch, I'm sure, but...
Magical armor, with a lesser encumbrance, doesn't allow non-proficient classes to wear it; but the actual structure of the magical armor is the same, whereas with these sets of armor we're specifically pointing out the fit and finish of the armor as being more advanced.
As a supporting point, Munition Armor, specifically noted as cheap and unfitted/mass produced, follows the standard AC=Stone method, and could not then fall under the Narrow armor restriction.