Absolutely - I was told by the police that an order lasted 3 years longer than any of the paperwork I had from court. I queried it again with them & they told me not aggressively, but certainly not politely, that they were right & to ignore anything I had. So I decided to wait until nearer the time before going through my solicitors because from a tentative chat I was quoted around £700 just to review this, & there wasn't a desperate rush to do it til the end of the period.
But in the meantime the police personal changed, & my first contact with the new person was a very polite admittance that they were wrong, & could I pop in to sign the paperwork so they could confirm the correct period.
So, yes it does happen. But in your case, no way would I just ignore their advice. If the area involved is one that is a pain not being able to go near (as in it's on the way to the shops or whatever, rather than somewhere that avoiding is no hardship) politely ask them to confirm where they got the 4 years from, ideally showing you the correspondence as you can check who is wrong here - could be they were given the wrong data from court, the period may have been altered at the last minute or if you have made a mistake, better to find out this way than the hard way. But get something in writing & stamped though