Evnow, why don't you go and read up on it, it's all in the Wiki and on the forum. Stoaty should be commended for all the hard work and effort that has gone into the model. In absence of something better from Nissan, which may or may not come, it's the best thing we have to estimate how the battery will do in different conditions.
Yes, Gids are not accurate and should not be relied upon. Our problem is that we don't have much data, and what we have is not very reliable. You probably know this better than anybody. This doesn't mean that significant trends cannot be spotted, and we are not able to predict certain outcomes, such as battery life, in broad strokes.
While your datapoint is certainly appreciated, I would not go as far as claiming that the model is 150% inaccurate. If you combine that with the off-the-cuff remark you made earlier that the battery will only show significant degradation in the deserts, it's becoming apparent that you must have spent close to zero time looking this topic this summer.
If you have a better idea how to approach this or wish to improve the model in a significant way, I'm sure that your contribution is very welcome. I would refrain from taking pot shots and making self-serving remarks however.