One thought just occured to me:
Could your 'speckled' cories possibly be Sterbai Cories ?
Even though they are generally regarded as a peaceful, community tank-type fish, they are nonetheless very active, fully omnivorous and liking protein in their diet.
At times I have read that they can tend to be a bit aggressive, and on a couple of occasions I have read that they are the only strain of corycat that may not be considered to be a fully compatible tankmate for discus (with the possible exception of Pandas - which are more delicate and may not stand up well to the higher discus temps).
I've kept at least a half dozen strains of Cories with discus, with the exception of Sterbais, and have never witnessed a whisper of them going near discus.