I see this regulator also generates mid-point common, making a virtual ground from the floating battery pack.
There's no current-limiting resistor for Q3 E-B/CR2 so any monkey business causing the -6.7V rail to go more negative i.e. battery (+) short to COM (holder) would damage them.
I would just lift the legs on a few parts and diode-test check them, full analysis is fun but a repair can go quicker just doing quick tests.
OP do you have an R22? The ECN Change 3 is confusing, I think they added it:
"Remove resistor A1R22 (390Ω) from collector of A1Q4." {should be add it?}
"NOTE: A Printed Circuit Board 00427-66501 with revision c or beyond has A1R22 added in collector circuit of A1Q4. Resistor A1R22 was added to reduce power dissipation in A1Q4 during overload."