is their reliance on time of day as the key by which program schedules are determined if a sports game runs late or if breaking news forces an interruption in normal programming the epg does not reflect the change in accordance with one aspect of the present invention watermark data identifying a program is decoded from incoming video this information is then checked against program identification data in the epg and if a discrepancy is noted then a change in the programming is indicated on the displayed epg consider superbowl sunday the epg database may indicate that a superbowl broadcast on channel 2 is scheduled to end at 5 00 p m at 5 15 a watermark is decoded from channel 2 and conveys an identifier associated with the superbowl indicating that the superbowl program has run past its originally allotted time the epg can update its entry for the superbowl extending its ending time to 5 15 the current time 5 30 the next half hourly interval or otherwise mark it as changed data for subsequent programming on that channel can likewise be treated as changed e g by pushing back all programming 15 minutes or to the next half hourly interval or otherwise and displayed in the epg accordingly continuing this scenario assume the superbowl broadcast ends at 5 20 this ending.