I think a lot of data is now held centrally. The police can enter your car registration number and find out if the circulation tax has been paid, it has a valid insurance policy and if it has a valid KTEO certificate. I don't know specifically if the emission certificate is stored centrally but if you are stopped by the police they will ask to see the KTEO certificate. If it is dated more than 1 year ago they will ask to see the emission test certificate. I have been randomly stopped by the police a couple of times, not for any offence, and they requested all documentation and they checked it all.