Sometimes if your cakes are super dried out it really slows down the pinning and mushroom fruiting process.  You might try doing a 12-24 hour dunk on a few of them and see if that does the trick.  I generally use a unopened bottle of spring water for that purpose.

(edit: I use perlite which holds up very well to long dunking times but if you use vermiculite instead you may not want to dunk for that long because vermiculite can sometimes crumble easier if you soak it for too much time.)