I would be interested to know how the data is stored. I understand that it only retains 28 days.
Basically it’s on a chip on the card.
It simply keeps storing data till it runs out of space then deletes oldest entry
The requirements are it stores a minimum of 28 days so it’s not a rolling 28 days, it’s till chip starts getting full which may be anything up to a few years depending on how much data it’s had to save per day
Just try go back for printout and you’ll be surprised how far back it does go
Incidentally DVSA can only use last 28 days info so any infringements past this time are ‘Forgotten’
Unless in major major accident then no doubt they’ll be dragged up!!
I wouldn’t worry about how long it stores personally just let it do it’s thing
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It stores a lot more than 28 days. Mine goes back to 16th Oct 2018 and I drive 5 days a week so its got plenty of info on there.
Sorry, it doesn’t forget all your infringements if you take a month off, but as mentioned DVSA / VOSA would. 
In essence, what it is storing are “events” - for the most part mode changes. As a result, the card of a driver on multi-drop around a city centre will fill up much more quickly than one used by a driver who does trunk runs. Once the available space is filled, the oldest events are overwritten. The available “event space” is quite generous, so for the vast majority of drivers, this means that much, much more than 28 days’ worth of events are held - even if they change mode every few minutes of every day.
Mines still got data on it from December so it’s significantly more than 28 days. If you’re trying to hide something you’re best off with a new card.