I'm partial to 45's but do not have a Jubilee model. However, I believe that these were assembled from the latter half of 1980 and going by your 0166, I would suspect this commenced in either August or September. It is conceivable that the date coincided with the month M&G was incorporated back in 1890. There was a nice feature on the history of the company in Guns Review at one point, a long, long time ago. Anyone got It?
My theory: 1980 was a big year for the 45 so they would have been producing large numbers of 45 component parts right through the year. By late summer, the requisite number of parts would have been pulled into a separate hall and stamped/ modified for the production of the Jubilee model.
They did a 35 Jubilee for continental Europe. Think it was based on the Super.