For an explanation of why it's officially called and trademarked "1K" and "Premier Executive 1K" vs. 100K or 100,000 Mile Flyer...see Post #3 in this thread of almost 4 years ago:

1K? Puh-leeze

Today when you see "100K" on manifests, agent's screens, and on boarding passes...that's just more of a "longhand" display of the 1K designation and marketed trademark.