What Happens Between the End of Tomb Raider III and the Start of The Lost Artifact?

“Only minutes have passed since the hideous creature that Dr. Willard had become gasped the last breath of its violently short life cycle. The experiment had failed, the gleam of immortality returned to the stars from which it came.
Lara looks on silently, oblivious to the press of the bitter Antarctic wind. Suddenly a ragged figure emerges from the dark, gaping hole of the meteor cavern-it is Willard, a human reborn, but in the throes of death. A hand gestures wildly, a final guttural laugh tears through the silence, the figure slumps forward and is still.
With the snow already forming a ghastly shroud over the body, Lara quickly tears an object form the dead man's grasp. A wallet, its monogrammed "W" now standing sadly against Willard's last earthly remains. Inside, the usual collection of tattered mementos, a hodge-podge of foreign currency and. . . but this cannot be! A familiar expression glides across Lara's face-an eyebrow raised by a wry and knowing smile. Before her, a telegram urging an immediate return to take possession of another artifact now secure beneath the Scottish mists at Willard's Loch Ness estate.
"The adventure continues," says Lara, to nothing but Willard's dark laughter still ringing in her ears. "So there was a fifth…" - Credit to Stella’s Tomb Raider Site for this.
Though I never mention it in the video, I noticed that the achievement for finishing The Lost Artifact is called “So There Was a Fifth…” written exactly as it is in the connecting text. Kinda makes me wonder just how many people they think saw that back in 2000?