The trouble with terrestrial software updates is they are not transmitted all the time, As the manufacturers have to pay for airtime on the multiplex. So they tend to be transmitted for a week at the most. As such if you miss them it is usually not transmitted again. So it is important to switch on automatic updates on freeview equipment.
Here is a link telling you what downloads are available for the following week.
http://www.dtg.org.uk/industry/download_schedule.php