I specified that I used cheated characters (rather than look for saves with characters at that level with iron handy), in case that made a difference (I have not tried very much crafting).
Sharpening the level 18 swords resulted in damage 185-299 or an unchanged 204-329. The level 17 swords sharpened to 175-283 or an unchanged 193-312.
With Crafting level 5, the lower damage range for each character level got a +2 Strength bonus when created on the anvil.
