a competition i once went to didnt have any voltage limits, but instead a cell count and cell size limit. for example, i couldnt have more than 5 cells of type C. to have a voltage requirement can be somewhat ambiguous, as you noticed.
batteries are actually rarely at the rated voltage. at full charge, it could be ~20% higher, and at full drain perhaps ~20% below. if they say 9.6V, I would assume they mean the voltage rating, and not the actual measured voltage. a 9.6V will be allowed.
if your battery is 4 years old, consider getting a new one. the older batteries arent nearly as good, and if you didnt take good care of your NiCad, it might not be so good anyway.