If there was any doubt that the property went missing during the assault, then (as long as they have recorded the assault as a crime) they may well have listed the property as lost. If nothing has been listed as a crime then they are out of order.
Write to the Chief Superintendent, detailing the incident, the report made and any reference numbers / shoulder numbers / names of officers involved.
Stress:
(a) you want the report properly classified as a crime (and to receive an appropriate crime number and update on what (if anything) they propose to do about investigating it)
(b) you would like an explanation for why the crime was not recorded as such and, should you not now be pursuing the matter, the crime figures would be incorrect
(c) ask if it is a deliberate policy to inaccurately record crime allegations as you are aware of another similar situation where a theft from the person was initially recorded as property lost (there is another thread on here from about 4 weeks ago but I can't find it at the moment - using the search facility here is not a strength!)
(d) that unless you receive a satisfactory answer within 14 days you will be making formal complaint alleging improper crime recording practices to the Professional Standards Department and the Independent Police Complaints Commission.