CONEC and CONET subroutines are relics from the old days when all dynamic models were called from them. I believe PTI introduced Table-driven dynamics in the end of the 80's, beginning with the plant models.
Nowadays more or less all models are table-driven so there is really no need for CONEC and CONET. However they are still there for backwards compatibility with old user-written models that are still not updated to be called directly inside PSSE. Still there are some wind models using the old way of calling models through CONEC/CONET.
From rev 33 there is no real need to call models in CONEC/CONET, all user models can be rewritten to Table-driven dynamics, for example as a miscellaneous model.
So, in short, don't bother about the existence of CONEC and CONET. Activity DYRE will inform you if any of your models is called from CONEC or CONET. If so, you need to compile the subroutines and create a new dsusr.dll.