When Larry Hagman and Susan Anspach board the plane to search for the 2 Million Dollars, Larry is wearing sandals and socks outside the plane, the next shot inside the plane the socks have disappeared!
During the initial helicopter pursuit, Sam remarks (of the heli he is chasing) "all its numbers have been painted out". But the registration number on the underside is clearly visible in several shots.
During the initial chase sequence the helicopters are seen flying down a busy street at low level, but in onboard shots (looking rearward) the street is totally deserted.
The aircraft graveyard would have had some kind of security patrol. The unexpected arrival of the four helicopters and the subsequent events would not have gone unnoticed.
There are several sequences involving people walking around the helicopters with the rotors turning, but no downwash or turbulence is evident.