If you have two examples then they wouldn't be rarer (if you are referring to being rarer than my chips) as there is only 1 of each color of the CPRs.

I believe that the Casino de Puerto Rico opened for business right around the time that the CPR chips were ordered (1923). It is common that the issuance date of c&s corresponds with the opening of the casino. C&S were usually the first type chip ordered. A casino wouldn't normally start with a large key mold, then reorder with a c&s. Later on casinos would opt for less expensive chips. Someone (maybe Charlie Kaplan?) sent me a photo of the Casino de Puerto Rico with the opening date. I'll have to locate the photo.