I know this might be taking the conversation in another direction, but it might be reasonable to conclude that Lab Texts are fantastically expensive based on build points.
A level 40 spell costs 8 build points. That's the same as 40 pawns of vis as vis stocks (or you can go the other way and vis stocks are fantastically cheap). Could those vis stocks be used in trade to acquire lab texts for needed spells? I suppose one way that the high price can be justified is if the PCs are designing the library of texts for their own specialties, so that they mesh perfectly. But if the players are generating a lab for verisimilitude then I would focus on granting more free build points for certain important text such as Aegis of a couple of different levels, Wizard's/Ritual Communion of several levels and then several other common spells from Romer's Book[1].
If you're designing the lab texts as the SG, I'd probably just put what I want and charge some fraction of build points to account for it. And then you can tweak it to have a few spells they can learn early and a few spells they can reach to acquire in a few years.
[1] I'm a player in that saga mentioned in the linked post, and there's a house rule reducing the cost of lab texts. Although this rule is for use in play and not necessarily covenant design using build points, I think it's a good rule of thumb to use when determining what kind of library of lab texts a covenant that exists should have...