IN Express Additions #4, I made it clear that each Vocational Kit should only give half of the Codex or Folio.
So, I ahve gone back to the core rules and added errata for the Arcane and Hybrid kits now as well - so that the Kits themselves specify this....
i.e. if you take the Wizard Kit only once, you only get 15 of the spells from the Wizardry Codex
also If you only take Bard once, then you only get 6 of the 12 spells that belong to the Bard Folio
In each case, the spells seleted are the player's choice. (and there is nothing that says that they must be chosen at the time of casting.
This falls into line with the Expanding Magic section of Express Additions #4.