I don't think there is
On the Garmin standalones they fully remove the previous map files and replace them
I suppose a dealer may be able to check the capacity, 9r there may be a way of looking in the engineering menu
Thinking back though, I think I had that 1% once but after reformatting and re-downloading it was fine. I've always ignored the Garmin Express message about 'we've got it from here' and wiggled the mouse every so often to stop any screen saver kicking in as that can interrupt it.