I think the reason that SSB isn't super well documented yet is probably because the protocol is still subject to change and not yet set in stone. I think Manyverse tweeted something about how SSB might get mutability and a delete propagation message in the future even.

Regarding "degrees of separation". I think it makes sense to have the degrees be

1. "I have met this person in real life, known them for a long time, and can confirm that they are who they say they are".

2. "I only know this person through the app, but we both like and respect each other and are friends"

3. This is either a 1st or 2nd degree relationship of one of my 1st or 2nd degree relationships.

So theoretically 1 and 2 are the same, the difference being you like scanned a physical QR code verifying 1 and know them IRL for example.

That way the degrees can double as a "web of trust" that serves as identity verification.