here that (what I call) the first four Captain Flandry stories form a coherent tetralogy. However, unusually for him, Poul Anderson also wrote a partly inconsistent prequel (see here). In The Day Of Their Return, set earlier, Terran Naval Intelligence learns of Aycharaych's telepathy even though, at the beginning of the second Captain Flandry story, Dominic Flandry, a Terran Naval Intelligence officer, does not know about it.
It is always possible - and enjoyable - to try to iron out even the most glaring inconsistencies in a fictional series as Holmesians, who included Poul Anderson, know. However, the simplest explanation of this particular inconsistency is just that, although Anderson did revise some of the Captain Flandry stories for later republication, it escaped his notice that the later written prequel necessitated one specific revision of "Honorable Enemies."
Some texts are finished products, perfect and complete with not a word out of place, whereas others remain works in progress even after publication. An example of the former is Pride And Prejudice, although even it was enhanced by gestures and facial expressions added in a high quality TV dramatization. An example of the latter is Hamlet which means whatever a theater company can make it mean in each performance. I have seen one short dialogue given diametrically opposed meanings without the alteration of a single word. Shakespeare revised plays between performances. However, as soon as as an author has died, his texts become fixed, although their interpretation and reinterpretation continue.
Any unfinished or on-going series is a permanent work in progress. Thus, in Anderson's Technic History, "Diana, Daughter of Dominic" remains a proto-series because Anderson needed time to write some less space operatic speculative fictions. So we can try to iron out the telepathy contradiction or can just accept that, massive though it is, the History of Technic Civilization remains a fascinating work in progress.