wasn't it pretty much confirmed that Thorned Namcial was there?
Harry leaps to that conclusion from a standing start and Mab says nothing either way.
Harry then sfaicr, never mentions that again in any book after SmF, even ones crawling with Denarians or set largely in Winter.
Considering that the
other conversation Harry has with Mab in SmF turns out to have involved her messing with his memory, I suspect she's got something going on there. (Hiding that whichever Denarian blew the doors off Arctis Tor killed all the trolls and goblins to open a pathway for Harry and company to get in and take out the Scarecrow without them realising they were being played is still my favourite notion here.)