I've investigated this a bit more, and discovered this document:
http://www.freeviewnz.tv/media/1055/freeview_dtt_transmission_rules_2_1.pdf
Section 5.12 describes the New Zealand EIT schedule. I've quoted a bit of it below, and it looks as though TVHeadend would have to be able to parse both the EITSchedule Actual and Other tables in order to fully populate the EPG for viewers on the non-Auckland multiplexers in New Zealand. Is this currently possible, or is it something worth putting in a feature request for? I'm guessing it would be less work to implement than feature request #3783, which asks for an MHEG-5 EPG implementation :)
"To limit the EITschedule bandwidth broadcast on each multiplexer, EITschedule_actual
and EITschedule_other tables are activated on Transport_streams;-
0x19 TVNZ Auckland multiplexer,
0x1d TVWorks multiplexer
0x21 Kordia multiplexer.
The TVNZ regional multiplexers transport_stream_ids 0x1a, 0x1b and 0x1c are deemed
identical to transport_stream_id 0x19 since they are made up from exactly the same
service_ids, event_ids and associated CID data, differing in advertorial content only.
EITschedule_actual data is not activated on these multiplexers.
For a PVR device to fully populate its event information database with every Freeview
services event_ids, irrespective of its‟ current active multiplexer it must parse both the
EITschedule actual and other tables. If the database includes duplicate service_ids
irrespective of their transport_stream_ids it shall discard the service_id with the lesser
signal quality."