Going back to the source... it was a question of part numbers reflecting construction differences, when they actually denote the third and fourth generation drivetrain design.
There would have to be enough power left in the drive battery to power the reverse movement. If I remember correctly the smaller "starter/generator" motor can directly crank the ice but has to have power from the power booster/invertor. I don't know in an emergency if it could boost 12v to the 3 phase of the motor. I suspect that under gearset at rest maybe only one of the three field coils would be needed or maybe all three since cranking is at low speed so maybe 12volt battery could handle it. ( I believe based on picture of 12v I saw it was a "spark-a-lot" brand ??? Which appears to be an AGM battery which will support higher charge/discharge rates than liquid lead acid battery" so maybe). I further expect (from lithium-ion battery info in general) that at some SOC (state of charge) (let's assume 20%) the drive motor is not allowed to run probably due to its size. The smaller "starter/generator" would haver a lesser draw and would be allowed access to the drive battery down to SOC (let's say 10-15%?) and start ice. Once the ice is started the starter/generater will reverse polarity (gears always turn same way) and start charging drive battery. It is not real clear to me at this point but I believe that with the ice running and the small motor is splined to the crank shaft and is supplying current to the booster/inverter the drive motor now has power to run in reverse and back the vehicle up. There is a gear that is split which has to do with drive and reverse I believe. Reverse can happen when some gear is held sorry but I havent visualized this function yet". Dang that will take 3-4 hours!
