I Knew It: The end of Mission of Honor features Haven and Manticore allying against Manpower and the Solarian League. This had been predicted by many readers.
Its Pronounced Tropay: Word of God is that "Manticoran" is supposed to be pronounced with the emphasis on the third syllable (as "Man-ti-CORE-ahn"). However, all the audiobooks incorrectly put the emphasis on the second syllable (as "Man-TIK-er-ahn"). As it turns out, the fault lies not with the narrator but the author, who accidentally gave her the wrong pronunciation for the word in one of his emails. After the mistake was cleared up, it was decided that the incorrect pronunciation would stay in the sequels to avoid confusing the listeners.
Dr. Janet Frazier in At All Costs is an obvious nod to Dr. Janet Fraiser of Stargate SG-1. Weber confirms this in an interview and explains that he was upset when the character was killed off in the show and decided to bring her back.
What Could Have Been: The Honorverse was originally going to be timeskipped several decades, following the death of its namesake character during the climax of At All Costs. Her children would have continued the action. The Eric Flint collaboration Crown of Slaves nixed this plan; its espionage plot ended up fast-forwarding the conflict by putting pressure on the Mesans to enact their plan early. As a happy side effect, Honor was spared, cutting off what would probably have been the greatest fan rebellion in modern Sci-Fi literature.
Word of Gay: Word of Weber is that Admiral Mark Sarnow is gay (and happily married), though the mention of it never makes its way onscreen. One forum poster did, however, note that it could potentially explain why Pavel Young never accused Honor of sleeping with him.
Write Who You Know: In A Beautiful Friendship, the Harringtons have a meeting at a restaurant called "The Red Letter", owned by a person by the name of Eric Flint. The fictional Flint is said to hail from the world of New Chicago, described as "a dumping ground for radical anarchists, socialists, and - especially - every member of the Levelers’ Association the government could round up after Old Earth’s Final War". The Real Life Flint, an occasional co-author with Weber in this and the 1632 series, is a self-admitted socialist, and currently lives near Chicago. Also qualifies as a Shout-Out.
Honor's actions in The Short Victorious War, assuming command of the fleet after her admiral is incapacitated, rather than having an admiral aboard another ship assume command during a key moment in the pitched battle, is likely based on the actions of US Navy Lieutenant Commander Bruce McCandless aboard the heavy cruiser USS San Francisco (CA-38) during the Naval Battle of Guadalcanal. Like Honor, Commander McCandless was decorated for his actions rather than court martialled. With the death of Admiral Dan Callaghan, Captain Cassin Young, and San Francisco's XO (as well as Admiral Norman Scott aboard USS Atlanta, accidentally struck down by friendly fire from San Francisco, nobody was immediately aware of it in the confusion except a the men who found Scott's body), the US fleet was in disarray. He was not the seniormost surviving officer aboard San Francisco. The senior surviving officer aboard was Lieutenant Commander Herbert Schonland, the ship's Damage Control Officer. Schonland was far too busy keeping the crippled cruiser afloat, and told McCandless to "carry out the Admiral's orders," effectively giving command to McCandless (though necessary, this could have been interpreted as Dereliction of Duty and/or Deserting his Post In the Face of the Enemy for Schonland). When the fighting subsided, Captain Gil Hoover of the light cruiser USS Helena took command of the remaining ships as the senior surviving officer afloat. Though costly, the battle was a victory for the Americans, and McCandless and Schonland's actions saved San Francisco, with both men receiving the Medal of Honor.