Sometimes they just update the data because they received new data. I don’t know what their policy is for checking data they get from vendors. If it’s like my company, upper management decided, to save money on hiring quality inspectors, to expect the vendor to deliver good parts 
… egad 
For instance, they talked about how they upgraded the DEM data for the US update. In my eyes, I liked it better before the new update around where I fly (Northeast). But, I can’t quantify that totally. But, for example, It seems like parking lots all became small hills bounded by their edges. And buildings (that I used to use for landmarks in the pattern) that used to be spot on disappeared and became pictures on the ground. I have submitted examples of this to Zendesk, and it’s been marked solved. If fixes get integrated in the next year, I’ll be happy.