The non-available nodes a query weights, on each bracketing map that has any.

earlier is the earlier of the two maps bracketing the query epoch, or the only map; later is the later one. Either is nil where that map's weighted nodes all hold values.

The same struct is the degraded status field of a value a :renormalize policy produced and the payload of the {:nodes_not_available, node_gap} refusal a :strict policy returns, so one match reads both.