The Raleigh Olympus was produced in two versions. The early Mk 1 was produced between 1970 and 1976, although in the final year or two Raleigh were beginning to cut corners in the spec, the main change being the move from Bluemels All Rounders to Bluemels Populars. Another thing to look out for are the disappearance of the fork thimbles and brazed on pump brackets instead of the chrome frame clips.
In around 1977 the Mk 2 was released, called the Olympus GT5. It was of course just a giant retrograde step, being heavier and cheaper than the Mk 1. The paint was plain flat blue as opposed to the beautiful metalflake of the Mk1 - and only blue was available. The mudguards were cheap heavy steel pressings - and I'm guessing it was about this time that Bluemels became part of SKS and went to Germany. This probably put cost pressure on Raleigh so they began producing cheap steel mudguards inhouse. The Mk1 and the Mk 2 are very different bikes, with the Mk2 being little more than a product designed to fill a price point for Halfords.