Is there any way that NCM will see that the config hasn't changed from the previous pull and not generate a new copy of the same config?
Having the last 25 days of configs isn't helpful if the one change in the last year wasn't 30 days ago.
If you're using NCM v6 go to the software console and there is a checkbox on the "Download Config" tab of the "Edit Job" dialog box that says "Only save configs that have changed". I suspect this will do what you are asking.
If you're on NCM v7, afraid I can't help as I've not upgraded... yet!
In both NCM 6.x and 7.x when you run a download config job, there is the option in the Download config tab to "only save Configs that have changed"