In some instances, historical invoices that were not created with revenue recognition records will cause a downstream credit memo to also not be associated with revenue recognition records. Do the invoices, the credit memos were created from, have revenue arrangements, elements and plans associated with them?

Yes the invoice from which the credit memo was created contains an opening balance item that was directly posted (direct posting). However, in the sandbox, when I reproduce the test and create a credit memo from the same type of invoice, I remove the original item and replace it with one that is properly configured for revenue recognition. In that case, a revenue arrangement is correctly generated. So it seems that the behavior depends on the item used in the credit memo rather than the original invoice alone.

That would be a preferred work around. Would need to match the rev rec period of the original invoice or recognize the CM in one month if the original period was fully recognized.