Cycle route symbols

Morning all!  I'm relatively new to road biking, and stumbled across this site for route planning - it is excellent.  I have some questions on the symbols used for predefined cycle routes, and was hoping for some insight into those I don't understand.

The red rectangular boxes I understand are NCN routes, with more info on sustrans.org.uk

The some of the light blue rectangular boxes are labelled 'NB', which I understand is 'National Byway'.  But some contain a number, for example '52' near Maidenhead.  What are the numbered routes, and is there a reference site for these numbered routes ?

Finally, there are dark blue boxes with Euro style gold stars, some numbered, others with letters.  Again, if someone could point me at a site that gives more detail on those routes I would be most grateful.

Thanks in advance for any help!