So if initially had 2 wedges simulations setup and I cached out the data , then decided to add a 3rd one , do I have re sim the data for the previous 2 during the cook or can I leave the cache files for those alone and just cook the cache for the newly added 3rd one ?

If the Cache Mode parameter on the ROP Fetch TOP node is set to Automatic, the work items will pick up existing cache files on disk assuming they haven't been invalidated for other reasons (such as upstream work items writing out new outputs). Work items that cook from cache are marked as cooked immediately, and won't actually be scheduled for cooking.

Ahhh ok ,thanks !