I discovered a little glitch sometimes when the pre-required skill is not in training Queue the injected skill books do not appear at Skill Catalogue.
Example my Hull upgrades is Lv 3 not on training queue , I purchase all 4 of the Armor Compensation skills and mass inject them all 4 they do not appear at the skill catalog at the armor branch but they have disappeared from inventory , next step I move the Holl upgrades skill to be trying to level 4 at the training queue , , at that moment the 4 skills appear at the skill Catalogue
I can reconfirm that in order for a skill to be visible that is being injected at the skill catalogue the pre required skill needs to be in training queue being assigned to train all the levels that are pre-required for the skill that is being injected into the skill catalogue , otherwise the scale book will disappear from the inventory being injected but invisible until the pre-required skill is in training .