Q20.102. LNER A4 MALLARD World Record Plaques.

I have been collecting model trains of the LNER most of my life and have a model of LNER A4 No. 4468 MALLARD, which as we know holds the land speed record of steam traction.
I posed this question on the LNER Society Facebook page and was directed to speak to the RCTS.

 My question is:

When did Mallard first receive/wear its World Record plaques?   (Damien Gorell, Townsville, Queensland, Australia)