Hello. I've looted 30-40 strongholds in my search for ancient tomes and noticed that there are some ancient tomes missing.

I have between 4 and 15 of some and 0 of the others. These books exist in creative but appear not be obtainable in survival.

Those are: Protection, Blast Protection, Fire Protection, Projectile Protection, Respiration, Depth Strider, Frost Walker and Soul Speed.

Is this intentional or just a bug? If it's intentional, could you please add it to the Ancient Tomes section of quark's features on the webpage?

This is intentional, yes. It's also already documented in the site.