| When it comes to anything I put out in an auction preview post, if I give a Tier, I'm talking about its stats only. That's actually why the IC flavor text uses the phrase 'in crafter's terms' when referring to Tiers. It's a way for me to communicate stat ranges without adding in the full appraisal (which you can get via the in-game preview).|
Any additional things beyond stats are noted in the remainder of the preview information for that item. That's why you're seeing things in the auction that are noted as T5. T5 stats aren't normal auction level just by themselves, but because stat tier is added to other aspects to result in the item's final overall tier, T5 stat items can show up in auctions when other things factor in.
So to use the previous example, the battle odaj is T6 by stats alone.