Blue Diamond was a Norvell and Shapleigh trademark in the early 1900s I believe. Good razors and the ones I've seen had pretty scales on them.
Birko I know nothing about, but being a Solingen razor, I expect it is a good razor.

I'm sure there is a thread on here about the Robeson numbering system, as Ed mentions above, do a search for it to learn a lot.
The short version is that model 15-L-40 is the model number that "fits your face" for "tough wiry beards and tender skin".
Check out RobesonsRme.com and click on the straight razor link.

And yes, the Robeson is a good razor.

Send them out to be professionally honed and start shaving.