It sounds to me as though you are not fully understanding how the car works out how far it thinks it can travel on a 100% charge.
It's not clear from your note, but I am assuming that you are saying that on different days that you are seeing an ESTIMATED range that varies between 34 and 23 miles.
If this is the case, then what you are seeing, is BASED ON your previous days driving. The car is estimating what your next journey will be, if you drive in the same way as you did yesterday (or since your last charge), but it never is.
This does not mean that the actual distance that you can travel will actually be 34 or 23 miles. The actual range each time you drive is totally dependant on how you drive on the current charge.
For example, I have driven 42 miles on a 100% charge when the car has estimated that my range is only 24 mile. This was because I drove in a very economical manner. After driving 42 miles the car estimated that my next charge to 100% would do 42 miles, but it wasn't because I drove differently.
In general you can expect the battery to give slightly less range in really cold weather, but the last few weeks should not have been cold enough to cause too much difference.
I was told by the dealer that the "fix" for me was software (the car computer), however my range was initially far less than you have quoted so I do not think that you have the same problem. I was only getting 16 miles of actual range on a full charge.
For comparison, my current range is varying between 24 and 35 so it's in line with what you are seeing, so I think that there is no fault.
You need to be more aware of the actual number of miles that you get from each 100% charge, and not the estimated range.
If the car has been using petrol as well as battery, the estimated battery only range is always going to be unreliable.
A key indicator of actual battery capability (and how you have been driving) is shown on the electric information display shown as miles per kw.
For me with short trips around town I rarely get anything any higher 2.6 miles per kilowatt hour of charge, which means no more than about 24 miles of actual range.
When driving on the open road at a steady speed of 45 to 50 mph, the miles per kilowatt will be between 4 and 5, and gives an actual range of between 35 and 40 miles.
All of my driving information quoted here is based on using the "B" drive mode, with 100% regeneration, with no reserve for battery.
Unlike full electric cars, the Superb has gears which will affect actual range in the same way as with petrol. You will get less range if you are driving in low gears.
For me, the only way to prove if the car has a fault or not, is to drive on a road with no stops at about 45mph. This should give you somewhere between 32 and 40 miles before the battery is all used (set the option reserve battery to zero so that the battery is fully used before the car switched to hybrid auto mode).
If you can do the same route, in the same driving style, you should get a consistent result. If you then drive with lots of gear changes and acceleration, on the same route you will see a substantial drop in the actual distance travelled before the battery runs out.
This is how it is supposed to work, and cannot be fairly compared to an ALL ELECTRIC car which has only one gear.
Hope this helps.