Schools class nameplates

Looking at the 2009 Hornby catalogue I notice that all of the BR versions of the Schools class to be produced have a black background to the nameplate whereas all the SR versions have nameplates with a red background. This sparked my curiosity and set me studying my reference books. Richard Derry in The Book of the Schools 4-4-0s makes no reference at all to this point and as their are no colour photographs there is nothing of help. However Peter Swift , in Locomotives in detail Maunsell Schools class has this to say "Nameplates had a red background until 1952, when BR headquarters ruled that all nameplates should have a black background. This ruling was generally followed for main works repaints until the early 1960s, but many of the running sheds repainted the nameplates red."
This to me sounds rather curious on two grounds:
1) Running sheds with the time and inclination to repaint nameplates?
2) All nameplates with a black background. How many West Country locomotives lost their red background? and how many Battle of Britons lost their blue background? I think not!!

IN the book there are colour pictures of 30923 (front cover) 30926 (frontpiece) 30915 (p43) 30926 (p46) 30925 (p47),
30936 (p47) 30901 (p50) 30924 (p50) 30934 (p51) and 30928 (p67) with red background plates. Total 10
With black background 30912 (p34) 30905 (p35) 30919 (p42) 30910 (p43) 30932 (p46) 30902 (p50) 30913 (p51)
30911 (p70 + 71) 30937 (p71) Total 9

Does anyone have any further definitive information on this subject?

Regards
John Clements