When Jim leaves Millie's office with the roses, the woman he'll eventually hand them to can be seen waiting for her cue to start walking towards him up the hall.
When James and Millie are in Walter Holme's apartment for a drink before going to dinner Walter answers a call for James from their employer, but says "hello" long before getting the handset anywhere near his mouth and ear.
The 17th root of 9,355,126,606 is 3.8595114, so the next-greatest prime number is 5. If this were the actual problem, then Agnes was correct. The error was Elwood saying "nine trillion", when it was actually "nine billion"