I guess to summarise what I was saying. Yes, it's generally accurate ... but sometimes for an individual property, there is a factor at play, that there system doesn't capture, that decreased (or perhaps increases) the value of a particular property.
For example, two identical properties ... on the same street. One might back onto a ravine, while the other only backs onto other houses. The first would have a boost in value that would not likely be captured in their methodology. So their property valuation would likely always be below the market value.
In my case, I bordered one alley, and my property was much higher than a second alley only 20 feet from my property, so we have a great view overlooking old garages, old cars, and two collapsed structures. I think it's great myself!! But it does seem to devalue the house ... and that's not caught in my valuation. Neither is my proximety to an artery (which isn't captures because I'm only very close, rather than immediately adjacent) ... yet I still see streetcars out of my back windows, and hear them through the front ...