CO items can be archived together with the origin object or independently of them.
If you archive them independent using CO_ITEM, then you cannot anymore easily jump from an archived Sales order to the related CO item.
You have to run the analysis as mentioned by Manjunath Ravi and explained in Table COEP (SAP Library)
to know what from where your CO items are, and then you may need to the business to decide together if you want archive it together with e.g. the sales order SD_VBAK or independent using CO_ITEM.
Even better if you could do a test in QA system and could then show the business how you can access in those cases, this may help to make then the right decision