There's also a timing problem. These two books show how Dr. M'Benga came to meet and later join the Enterprise crew, so they have to be before "A Private Little War," but TVAM has to be some time after "Journey to Babel" as well. In production order, that would be impossible since they're consecutive episodes. In broadcast order, they're only 9 episodes apart, which is a pretty tight squeeze given that Sarek would need time to recover from his heart attack and return to full health. Plus the book implies that more time has passed, or at least that's my impression.
Maybe Lorrah was assuming stardate order, which might indicate a significant span of time (3842.3 to 4211.4) between the two episodes, with only a couple of episodes in the gap (Bread & Circuses, The Doomsday Machine). Depending on how long you assume a "stardate" to be, that could be 3-4 months on our calendar.
Or maybe chronology just didn't matter to Lorrah when she was writing. The chronology of the Original Series is extremely elastic even today. It was even more elastic in the '80's, before the Okudas wrote their Chronology