I have just reunited someone with their cat after it went missing for 8 months. I took it to the vets to be scanned. There was a chip but the phone numbers and address were out of date. Fortunately their email was current.
Then I realised I had had a new mobile phone ages ago and never updated the microchip company for my own cat. 
Microchips are brilliant aren't they but only if the details are kept current. 