Wander00 and Nutloose:
Thanks indeed for the response. I wasn't querying blue wing bands, but whether yellow wing bands appeared before the advent of the DayGlo markings. Looking at that evocative Dave Welch photo of WB654 and friends, I can't see any evidence of a wing band there.
What keeps bugging me though is that it appears illogical to delete them on a training aircraft...
Cheers!