When is post-op radiation not necessary for completely resected ipsilateral neck node recurrence in a previously UNirradiated neck?

For example: Initial primary of early stage completely resected oral cavity or oral tongue cancer with no adverse features and therefore did not get radiation, but now with single node recurrence. The NCCN Head and Neck guideline (Ver. 1.2015, ADV-3) states observation as an option for "no adverse features" resected recurrence. Are these "adverse features" extrapolated from the primary setting or validated in the recurrent setting? (This is somewhat of a follow up question to #565)