R-6 means 31-75 Known, but if you found a box of 100 it would take it to R-5 (76-150 known) which is still "very scarce" as defined in the Official Guide.

It means a big drop in value for the owners of the 2-3 that were previously known. Also, the 2-3 previously known were all drilled, notched, or cancelled.

Nice find!