Hi
The council tax (admin & enforcement) regs 92 (SI 613/1992) covers this.
Reg 18 says that a demand notice must be issued for the year in question. It also says that if a person is liable for more than one property in the same year then they must be sent separate demands for each property.
Reg 20 says that the demand is an estimate assuming that all things will remain the same for the remainder of the year (hence ctb is posted for the full year in advance)
Reg 24 allows an adjustment notice to be issued where there is a change of circs (e.g. benefit is reduced) meaning that more should have been charged.
Reg 18 does say liable for different amounts for different properties within the same financial year so I am not sure if that would apply in this case but it surely must have been the policy intention that you always get different bills for different properties regardless of when the adjustment is done.
Does that help?