I spent the day doing more science on this. I looked at everything under the sun about the spells I am using and it seems that there is just no feedback in the game when attributes of creatures change with (timed?) reactions. So, they are currently working, but you wouldn't know that unless you did what I did and ran a bunch of fights in the arena for comparison. Also as someone else stated in another thread on the topic of world gen secrets, you must include their own [I_SOURCE:SECRET] block for every sphere or you wont see them used in world gen. I have yet to get them to propagate via world gen libraries, but that may be a fools endeavor. For now I will settle for a rich availability of slabs.
Also, it appears that megabeasts, and maybe semi-megabeasts get the ability to bestow slabs on their worshipers if they align in sphere, meaning you get a whole lot of dragon-fire slabs.
Also, also, it seems like for some reason historical figures which manage to get bestowed one slab, more often than I would have expected, manage to get bestowed a second slab for a different types of magic. In some cases I would say this can be explained by a sphere overlapping two or more areas of magic, but in many cases it seems that they managed to convince completely separate deities, often of a different sphere than the initial, to bestow upon them a second level of knowledge. That's pretty cool. On the more funny note, it also seems that deities can bestow slabs to creatures which cant read them if the spheres are just right, when that happens they end up getting placed on some bookshelf somewhere with no one the wiser to the magics they contain.