You don't understand it correctly. Models are supposed to fit the evidence, otherwise they're incorrect. That's how science works. Say you've gathered evidence of the big bang. You create a model for it. Then, suddenly, for some reason observations and measurements of background radiation doesn't fit your model. If that is so, you'll have to either adjust your model as to fit the data, or throw it away and build a new model that fits the data.
Yes, when you model the past, that makes sense. What AGW proponents use are models to project the future. But they are inconsistent with the data of the past. They don't fit it.
They are simply fantasies to try and lend "scientific" justification to a political movement.
