I recently received a 428 Hero-level, Timewarped “Flowform Choker” which I was quite happy to get, given it was the character I was on’s best stats. I went to add sockets to it with some Tiered Medallion Settings, and it told me that the quality of my Tiered Medallion Setting was too low to add another socket to it. I tried all three qualities of Setting, but none worked.
This is a fairly big issue, because it effectively lowers the item level of this neck compared to other necks that can have sockets added to them.