Within the auction house if you view Item Enhancements for legs and sort by iLvl the listing will not put the current expansion armor kids and spellthreads first, instead favoring lower ilevel Dragon Isles items. This includes things like Stormbound Armor Kits and Daybreak Spellthread at ilevel 610.
Edit: I’ll add a secondary issue as it is related, but not exactly the same. If you click on Item Enhancements - Legs category and Filter by Usable Only then only the Dragonflight Reinforced/Fierce/Frosted Armor Kits are listed on a level 68 character. Things like Temporal Spellthread or Frozen Spellthread don’t show up despite being usable by a character of that level. Also none of the legacy expansion armor kits or spellthreads are listed with that filter.