Is there a way to prevent DCR authors and approvers from receiving incomplete training tasks for documents in DCRs that they've approved?

No. From a risk-benefit perspective, our industry advisors say that authors and approvers should simply sign off their training tasks with no further action required if they consider themselves already trained on a document. The benefit of authors and approvers not having to click Perform and sign off incomplete training is not worth the risk of having to explain to an auditor why some people who have a document as a training requirement either have no completed training records or have signed off their training records in a different way from everyone else. The person being audited would have to know to trace back to the originating DCR and show that those people were authors or approvers. An auditor could view this practice as an opportunity for errors to be introduced into the process and want to dig deeper looking for problems. The lower risk approach is for each person with a training requirement on a document to have a signed off training record.