This is a flow diagram that shows why many crimes are not accurately recorded in the police recorded crime statistics. Firstly, made crime are not reported to the police or discovered by them. Among those that are reported are ones which are made-up by the public, usually for insurance fraud purposes or they assumed a crime took place when it never did, for instance losing credit cards on a night out. Then even if a crime occurs police deliberately or in error do not record it properly, or to use the jargon do not classify it correctly.
This leaves aside the complications of legal definitions, Home Office Counting Rules and Home Office Crime Categories which run rings around what may appear to be common sense.