It's not technically wrong (you just show arrows from P_A and P_B to P_AB), but it misses the pubkey delinearization that's necessary to avoid one party simply subtracting out the other party's pubkey and thus take full control of the funds (key).

I think it'd be a good idea in such a presentation to make the notation easier to read. Use suffixes (suffices?), and be consistent. For example a very common practice is to use capital letters only for curve points, and lower case letters only for scalars.

Similar notational details: you first correctly point out that concatenation is used and notated with || , but everywhere else you're writing H(R,P,m); a reader will not understand if this is meant to indicate something different to concatenation.

Typo: 'finaln'.