@Neil
Hotfix is only to help with the initial startup acquisition time and does not affect acuracy while navigating.(If a full bouquet of sats has been aquired of course.)
It's basically a database of the Sat Status at the time you switched the unit off or put it into battery saver mode.
Once the unit wakes up it quickly locks on to known sats by the process of prediction.
The data is in the GPX folder and I suspect in NVRAM as well.
Current Model 3490's GPX folder is totally different to 3790 (Converted or unconverted). This is due to different GPS Chipsets.
Another thing that I've noticed is that the 3490 does not give you message about lost satelites(like the 1300) when you go through a short tunnel.
I think that they've done some magic in the firmware.