RP3 = original propedal shock. It had three levels of propedal adjustable by the blue lever. You could not turn the propedal off or lock it out. It could be push modified by TF tuned to increase the difference between the three levels of propedal. This gave “almost no propedal”,”propedal” and “almost locked out”. I did exactly this and it improved my cove hustler which was a bit bobby with the stock RP3.
RP23 = the lever now has only 2 positions “open” and “propedal on”. A blue dial allows you to select the ammount of propedal you have in the “on” position. There are variants of the RP23 now with the larger air cans and with boostvalves
RPL = similar in looks to the RP3 but the 3 position blue lever gives “open”,propedal,and “total lockout”. There is no adjustment of the propedal. I’ve got one of these on my 100mm “race” bike. The ability to properly lock it out is useful on Tarmac climbs when i like to get out of the saddle. This shock was called the Triad when fitted on specialized bikes.
I would echo 1961bike and say if you can get one in good conditon then getting a RP3 is sensible. The RP23 was more an evolution than a revolution.