The house I bought recently was placed in the wrong council tax band when the system first came in. It was only just around the value it was supposedly worth on the date set for valuation purposes, April 1991, when I bought it last year. I recently appealed against the valuation, only to be told that my “proposal is invalid because it is outside the time limits prescribed by law”.
The time limit the valuation officer is referring to, as you’re probably aware, is six months. If you buy a house you can challenge its existing banding within that period, but after six months you’re stuck with it. Not many people know this! After that your band will only change if there is some material alteration to the property or your street is reassessed for some reason.