Batboard

I recently acquired a PM400 and am trying to reprogram it. I know my cable is good with pins 6&8 shorted AND I have confirmed this cable worked on a previous PM400. Question is, I am using R05.16. Is it possible that this radio was programmed with R05.17 or R05.18, and if so, would that prevent my R05.16 software version from communicating with it?
I also tried to access the "SOFTWARE VER#" from the menu on the radio, going to P2>>UTILITY, but I only see 2 options, PWR LVL and BKLT INT.

Thanks for any help.