If you're unsure whether a change needs to be reported, it's best to report it anyway. Based on available council records, you should inform the council immediately about any changes in your circumstances that could affect benefits or Council Tax Reduction. This includes changes in income, household composition, or address.
You can do this easily online through the Citizen Access Benefits portal. Providing timely reports helps avoid issues such as overpayments or underpayments. Remember, if you're not sure, it's always better to err on the side of caution and let the council know.