When Mrs. Hewitt is given the envelope with her husband's effects from the car crash, the envelope shows the date of his death as October 20, 1970. She later tells Joe Mannix that she and her husband had been married only about a month before this death. Yet when Peggy tells Joe information that she obtained about the Hewitts, she tells him that they were married on April 7 - which would place the date of the crash as sometime in May, not October.
The envelope with George Hewitt's effects shows he died on October 20, 1970 but the written phone message showing that Albert Tucker received a call from Hewitt on the day he died is dated July 20, 1970.
When Mannix and the others enter the gold mine, they encounter flying fox bats, a species that does not exist in the US.
Boom mike shadow visible on wall in Mannix's office as he was sitting down talking to Mrs. Hewitt after he was surprised by her waiting in his darkened office.
The tower communications to and from Mannix refer to a "Tango 473" but this doesn't match the Beechcraft Bonanza he was flying registered as N7854R.