Rather than checking for the "UNTRADABLE" flag at the top, you want to look for the "Unsellable" tag at the bottom. Gear gets added to the expert delivery permissions at the same time that "Unsellable" becomes "Sells for ...", which for capped tomestone equipment is when the tomestone cycles down to uncapped to make room for the new capped tomestone (X.0, X.2, X.4).