Credit: The MIDI Manufacturer's Association Forum
General MIDI defines several Registered Parameters, which act like Controllers but are addressed in a different way. In MIDI, every Registered Parameter is assigned a Registered Parameter Number or RPN. Registered Parameters are usually called RPNs for short.
Setting Registered Parameters requires sending (numbers are decimal) two Control Change messages using Control Numbers 101 and 100 to select the parameter, followed by any number of Data Entry messages of one or two bytes (MSB = Controller #6, LSB = Controller #38), and finally an "End of RPN" message
The following global Registered Parameter Numbers (RPNs) are standardized  (the parameter is specified by RPN LSB/MSB pair and the value is set by Data Entry LSB/MSB pair):
For example: RPN control sequence to set coarse tuning to A440 (parm 2, value 64):
101:0, 100:2, 6:64, 101:127, 100:127
So given the time frame and the fact that these are MIDI files, these RPNs were probably used to set the pitch bend range of the channels in GM sequences or for tuning/detuning tracks via Channel Fine Tuning or changing octaves or transposing a part in whole steps via Coarse Tuning.