Age identifiers (ie 53 / 04 etc) change twice a year in the UK; in March and September - so a '53 reg car would be registered sometime between Sept 03 and March 04 - if they are saying it is an 2004 car with a '53 reg then it was registered in January or February 2004. The actual registration date (or Initial Registration date)will be on the V5 document that comes with the car and it is this date that used to determine the year of registration when importing into Ireland