Numberplates seem to sell very well on this site.
https://collectingcars.com/
I’m assuming that one or more of the valuations was six figures? I’d say it could fetch that much on a good day. But as you say the prices of plates can vary massively when you’re into the 2/3/4 digit stuff.
Could certainly be worth more than £50k.
Give Collecting cars a call and see what they think.