If you have a 2013 model year car the chances are the SatNav data is from 2012 or maybe even earlier.
The question is, does this really matter to you? The update costs about £160 I believe.
I was driving my 2006 MY S-Type with 2006 SatNav DVD until earlier this year and didn't have any major problems with it. I gather there was a new DVD available which also updated the system's software and firmware.
Apart from the ploughed fields bit the only real niggle was that the SatNav didn't recognise some newer postcodes, and some new roads (mainly bypasses and upgraded trunk roads) were completely missing! However, on the rare occasions that this was a problem I simply used Google Maps on my phone or iPad when I got near to my destination.