A lot of the first season losses could have been solo runs. Even the fastest loss in history, Elizabeth I's Golden Ship, could have been a solo win. A number of the runs where the artifact in question was on the bottom floor, particularly in the Swamp (or Spider's Lair, etc.), could have been solo victories if the first player had:
1. started in the Room of the Three Gargoyles (Royal Gongs) and
2. gone straight to the Observatory and
3. avoided entering the Heart Room at all costs. (Actually, avoiding the Heart Room and its various reincarnations in general was a good idea.)
These runs (Henry VIII's Seal, Kamehameha's Pendant, and so on) are the ones that stick out in my mind.