At 1:01:57 the museum staff person said Rhodesia had become Zambia. This is correct if it's referring to the protectorate of Northern Rhodesia, which became Zambia in 1964. However, Southern Rhodesia became Zimbabwe in 1980. The region underwent several changes in this period, and the name "Rhodesia" changed scope too.
The identity of the accomplice is never discovered. Imagine what this individual must have had to do. That's pretty heavy, both personally stressful and criminally serious. In fact the character is merely forgotten - not even considered, even though the person could easily have been identified (Lewis actually hints at the answer) at the end.
The first theft is never adequately explained. What the characters conclude is counter to what's needed for the plot - the date and time of when the item was available don't explain how or when it must have been taken.