Some websites state that the data entry LSB of an NRPN/RPN is optional. This would allow for reduced MIDI data to change an (N)RPN, but this seems not defined in the MIDI specification. If this is allowed it could mean a device should only upon receiving the data entry MSB update it's internal state. That is, the LSB should be considered default zero unless an LSB is received before the MSB. BUT ! In most implementations the MSB is send before the LSB.