Is there a window in an item's "original" levels where scaling gets messed up, or is that an anomaly? Or is that simply an item that existed prior to the implementation of scaling?
Silver-thread rod is 26/31, but also 23/26, and 39/42. Not that I can find one in 30s at all, anywhere. Item scale ranges seem to match mob scale limits (same item is 58/60, presumably capping at 60). Plate is its own story, but 8/12 (+11 secondary) plate gloves (overlord, gothic, bloodforged, heavy lamellar, revenant) can take +14 stam chants and could be considered. Some item, like the bandit cloak and uther's girdle, seem glitched on scaling, as plate generally, but I'm not even sure the ideal level to farm 39/42 non-plate.
Even more complicated, monster scaling has some kind of threshold. A 39 in Hinterlands fighting Vilebranch Hideskinners is facing level 38 mobs. a 42 faces level 41. A 45 faces level 45.
I found the same "spread" of item levels others mentioned. I have seen items 9 levels below my character drop. I think there's something like 60%+ to drop according to scaling pattern (ivl+3 scaled, +5 unscaled matching the difference to your char level), then lower % chances each level away from that until about 6 levels changes the loot bracket. My best chance for 39/42 gear seems to be on a 42-44 character, but I can get it pretty often on 45.