These aren't intended to both be added to the LDraw search path at the same time. To the best of my knowledge, they are intended for two uses:
For the second usage, 48/ or 8/ is included in the part file itself prior to the dat filename. So, if a part has a large-radius circle, it can use 48/4-4cyli.dat instead of 4-4cyli.dat. The p/48/4-4cyli.dat file would then be picked up while processing the standard p part of the LDraw search path, not with a specific scan inside p/48.
Programs are free to completely ignore the 8 and 48 directories. If they do so, they will work fine (as long as they append the full part name/path to each entry in their search path while searching for the part, and don't just take the filename part).
- Replacement for standard 16-facet equivalents
- High/low-resolution geometry specifically referenced in a part
For the second usage, 48/ or 8/ is included in the part file itself prior to the dat filename. So, if a part has a large-radius circle, it can use 48/4-4cyli.dat instead of 4-4cyli.dat. The p/48/4-4cyli.dat file would then be picked up while processing the standard p part of the LDraw search path, not with a specific scan inside p/48.
Programs are free to completely ignore the 8 and 48 directories. If they do so, they will work fine (as long as they append the full part name/path to each entry in their search path while searching for the part, and don't just take the filename part).