Mullard was manufactured by Philips Electrical Industries of N.Z. Ltd, they were distributed by C. & A. Odlin Ltd. Currently there are 11 documented models.

Mullard was a brand that belonged to Philips, they were distributed and sold throughout New Zealand by C. A. Odlin and Co (Odlins) the timber merchants.  The Mullard name was retired and replaced with Fleetwood in the mid-late 50's

Through observation it has been noted by the author that the Mullard model code can tell you a bit about the set - it has three digits - the first is the valve count in the radio (including magic eye), and the last appears to be the year of release.  The middle digit seems to be the series of radio for that year - for example there is a model 520 and a model 620: the 6-valve version seems to be identical apart from the magic eye, so both have a 2 for (what we will call) the series code, the 5 and 6 represent the valve count, and both were released in 1940 - hence the 0.

Philips codes from 'the Mullard years' have absolutely no discernable meaning that the author has been able to find - so knowing the Mullard / Philips equivalent models means you can then find the year and valve count for a Philips model as well.  In this instance, the model 520 and 620 are equivalent to the Philips models 152 and 153.

11 Documented Mullard Models
1939ish Mullard model 531 'Long Distance' 5, with magic eye on some  Dual Wave 
1940 Mullard model 520 5, with magic eye on some  Dual Wave 
1940ish Mullard model 542 5 + magic eye  All Wave 
1940 Mullard model 620 5, with magic eye on some  Dual Wave 
1945 Mullard model 515 'Meteor' 5  Broadcast 
1945 Mullard model 525 5 4
1947 Mullard model 537 5  Dual Wave 
1949 Mullard model 567 5  Dual Wave 
1950ish Mullard model 420 4  Broadcast 
1952 Mullard model 402 4  Broadcast 
1955 Mullard model 735 6+magic eye 5