The GCxxxx waypoint identifier is just that, an identifier. It has little other significance, beyond acting as a unique common identifier.
Some GPSr units can only accept waypoints of six characters or less, so the generated ID has a maximum length of six. The GCxxxx ID is actually derived from the sequential ID number assigned to each cache page when it's submitted for approval. The first 2 characters are always “GC”. Originally, the next four characters were created by simply converting the ID number to base-16. But it became apparent that that scheme couldn't create enough IDs for the fast growing sport.
In April of 2003, a new scheme was put into place. All cache IDs after CGFFFF would be created using a base-31 scheme. The characters used for the base-31 conversion are 0123456789ABCDEFGHJKMNPQRTVWXYZ (the letters ILOSU are omitted).
When converting from a base-31 waypoint ID back to its original sequential ID, you have to subtract 411120, to account for the value change between GCFFFF under the old system, and GCG000 under the new system.