Flipping the input bytes breaks the incoming message and no NRPN codes work. In fact using original 1.0 & 1.2 eproms it looks like the VS already read the input NRPN correctly, based on watching the messages in MIDI-OX. I send it this message in this order from an Arturia BeatStep Pro in NRPN mode:
99 0 NRPN MSB
98 12 NRPN LSB
6 (*) DATA MSB
And it controls the Cutoff Freq just fine.