The position is that you are duty bound to tell the Official Receiver of any change in your circumstances (such as an inheritance, or an income increase) while you are bankrupt. When you are discharged this duty ceases.
However, if you are asked by the OR after discharge to provide information (e.g. if he/she had heard somehow that you had won the lottery) then you have to co-operate by answering their queries. But if your win was after discharge then the OR cannot take it. In practice this requirement to co-operate is mainly for 2 reasons:
1. The OR may find something which leads to a suspicion that the bankrupt did not fully disclose relevant information about their finances etc. at the time they became bankrupt or later during the bankruptcy; &
2. If the bankrupt has surplus income then an Income Payments Agreement is made, which runs for 3 years (i.e. for 2 years after discharge). This is where the information you've been given comes from, I think. Throughout the 3 years the OR can ask for updated information on finances, & this can lead to a change in the amount of the payments being made.