Thanks to Ide Cyan for bringing to my attention that the Doctor malapropped Londo's surname in the original first panel of Part C. (It's been fixed.)
Paul Andinach informs me that Londo's decision to ally with the Shadows came before Captain Sheridan arrived at the station (a datum which my specific net researches failed to turn up). Consider the anomaly an effect of the Master's presence in the timeline.
(If you didn't get Kosh's reference, "You know his story: you share it", you don't know the Doctor's father's stories. See a special Father story index.)