It is difficult question. For Finland I could see small addition like POI or changing traffic rules for each release. But as in your case Garmin do not hurry to update global roads network. But for example at one moment in version 2014.30 the full renew information was contained. I think Here (ex-Navteq) have own plan (time-stable) for serious global update of region but certain categories of update as new POI in its base or user reports be adding from one release to another. I think if you look at maps with more deep sight you can find a some minor additions or changes.