Lots of people operate under the mistaken impression that Clanners never conceal anything. Or are constantly broadcasting the truth of all things on all channels all the time. The truth is much more nuanced.
The Burrock leadership concealed their dark caste dealings. They just confined that information to people they trusted. The Wolves hid the devastation of their eugenics program after Tamar was hit by at least one nuke during the Jihad era. After the Wars of Reaving era, the Cobras hid the revelation that their eugenics program was compromised by scientist tampering (many genetic legacies corrupted) for as long as possible and worked feverishly to get more genetic material in the short term. Khan Bjorn Jorgensson was quietly a Warden in the days that the Crusaders dominated the Ghost Bears. His Warden side came out gradually through his leadership style of the Clan, and gradually it became more open as the Clan shifted toward Warden views. Ulric Kerensky played lots of games with his real intentions. Aiden Pryde concealed his identity for a long time. Falsified his codex and lived as a freeborn warrior. Years before Revival, the Jade Falcon Khans increased the number of sibkos in training, a reality that came out once the Khan had been devastated by the Refusal War and needed to rebuild quickly. But few seemed to know about it, even within the Clan.
Khan Showers was embarrassed to admit how weak Huntress's defenses were, once Taskforce Serpent took it and he had to go to the Grand Council to ask for help. So the other Clans thought Huntress's defenses were stronger. He was also then shocked by the revelation that the Jade Falcon science station on that world was also gathering intelligence on the Jaguars.
Kindraa Smythe-Jewel didn't know the Horses and Coyotes were embarking on a campaign to destroy them until they showed up and declared a batchall. But that coalition had been planning that event for a while.
We've seen many Trials between Clans where a unit was surprised at the composition/makeup of the opposing force in some way. Or where reinforcements showed up that weren't expected.
That's by no means a complete list. It just illustrates the point.
Yes there are certain levels and types of data that are meant to be open and shared. But often that only happens once you've initiated a Batchall. Even then we've seen accusations made that someone was misled. Other times a Clan only truly gains all the information once they've won a Trial and acquired the isorla, including personnel and equipment.
The book Warriors of Kerensky tells us that the Bloodname House leaders of shared bloodnames often make up for in information brokering (by gathering reports from their various Bloodname House members) what they lack in voting power in one Clan. The Diamond Sharks/Sea Foxes prided themselves on being the best at information gathering via their merchants. The Star Adders had an actual intelligence branch.
Such things would not be necessary if everything was truly shared all the time. That just isn't the case. Tradition dictates certain things are shared, but only when certain circumstances are triggered. The best known, best understood circumstance of this is when someone issues a Batchall and wants to know with what do you defend a target. You are supposed to then show your cards. But even then, it doesn't have to be everything you have, just with what you intend to defend the target.
Other times, the isorla of a Trial, such as the bondsmen/bondswomen taken, present their new Clans with their codexes and also to some extent share what they know about their old Clan.
We see things concealed all the time. We see people lie. In general the Clans TEND to be more honest and direct than Spheroids. But it's shades of different. It isn't a society that completely broadcasts every new development, every codex, every troop deployment, all the time. It's just a society that has a different set of criteria and circumstances for when/how tradition dictates you share information.
Zeroing in on what you said about codexes. I doubt they are shared all the time and continuously. Otherwise, many of the examples I laid out above would be simply impossible. You could use that codex data to constantly plot and update your understanding of the exact composition and location of every Clan warrior everywhere. Accordingly, you would be able to decipher where every Clan touman unit is. We know they don't have that information. Ergo, codex data isn't shared all the time. Just at certain moments and under certain specific circumstances as dictated by Clan law and traditions.