You're right that 8 wards is too small to claim statistical validity, and the calibration was derived from those same 8 wards. That's overfitting until proven otherwise.

That's exactly why we are pre-registered predictions for 136 councils on May 7. I'll publically announce our predictions on May 1st.

If the calibration generalises, we have something. If it doesn't, we have a well-documented failure. I hope for the former, I can accept the latter :)

So to summarise the 2 potential questions... Is it any good? Does it work? The honest answer is: I don't know yet.

The paper says as much. May 8 will tell us.