I assume you had the parts linked to operations but now you only have one operation the parts are not getting issued (backflushed).  If this is the case you could use the WO cost report.  It will show you what was on the actual bill and what you have issued.

Also if you want to do a deeper dive to check all your BOM's to routings to see if there are any operations on the BOM that are not linked to the current routing operations then you would need to create a very simple report that looks for and operations on the product structure (ps_op) that do not have a matching operation on the Routing (ro_op).  If you have multiple routings then also you would need to make sure you link it correctly in the report 

Phill,
  Thank you for your advice.  The report works good.