gistfile1.txt

A    B    C
 \   |   /
   \ | /
     D


D^  = D^1 = A
      D^2 = B
      D^3 = C

E'  E'' F'  G'
  \ |   |   |
    E   F   G
     \  |  /
      \ | /
        H

H^ = H^1 = E
     H^2 = F
     H^3 = G
H^^= H^1^1 = E'
     H^1^2 = E''

H~ = H~1 = E
H~2=     = E'
H~1^2    = E''
H^2~1    = F'
H^3~1    = G'

Is the ordering across the way of E', E'', F' and G' based on the order in which they were merged in, or the actual age of the commit?

I think it's the order specified in the octopus merge command, but I've never used it so I can't confirm that.