The manual says that if a mongo node gets too far behind and the oplog wraps then it won't be able to catch up and it will be stuck in that state without manual intervention.

I'm trying to write a script to detect that state and alarm on my cluster but it's not clear how to detect it. The link above gives a list of the possible cluster member states (as reported by rs.status().members[n].status) but it's not clear how you can tell apart "stale but able to catch up" and "very stale, cannot catch up". Are those states distinguished, if so, what do they map to or do I need to look elsewhere?