Eb is too young, Bob is nearly 700 years older than Eb, same with Kemmler, and we haven’t met Kemmler, unless he is the British Prisoner, but Demonreach appears to have been without a Warden longer than his last death.
I have Lea and Tam Lin with Tam Lin as the British Prisoner. Mab and Tam Lin is a possibility but this may be before Mab became Queen, and I am not sure the Lady’s Mantle would allow this. Mab appears first in literature and not myth, Romeo and Juliet, the Tam Lin legend pre-dates this considerably. The Leanansidhe myth also pre-dates the first use of the name Mab. Mab was riding with William the Conqueror around the time Bob was born, presumably at this point she was the Lady if she was mortal and shacked up with Merlin several centuries earlier.
We know from the Tam Lin myth how he escaped from being Winter Knight, what myth doesn’t tell is why or how he became the Winter Knight other than he fell from his horse and was captured by the Queen. Mab parallels him to Harry, what if he had to make a similar bargain? He became Winter Knight to escape Lea’s attentions. Originally Harry owed Lea, his debt was bought out by Mab who kept dangling the Mantle until Harry wasn’t in a position to say no. Harry may not be the first time Lea and the Winter Queen have played such a game.