Nm, I just watched the episode. No bag is left untouched. So that rules out the second flaw, but the first is still valid.

On the May 20, 1977 episode of "The Tonight Show Starring Johnny Carson," Peter Falk poses the puzzle to Johnny Carson and Ed McMahon. Johnny Carson thinks he knows the answer but Peter Falk begs him to not reveal the answer.

The facts are stated correctly. I believe some of the confusion about this puzzle come from the fact that this is a conversation between the killer and Lt. Columbo. Columbo interjects the weights, and what a penny scale is. The rest of the puzzle is stated by the "genius". The episode is S6 Ep3, entitled "The Bye Bye Sky High IQ Murder Case".

1 pound = 16 ounces. If there are more than 16 sacks it would be difficult (or impossible) to determine which sack has the phony coins. The scale reading would add whole pound to the result if the "different sack" is not one of the first 16 to be picked from.
btw-I am a huge Columbo fan;

No. If each piece of real gold weighs a pound then 16 bags should weigh 136 pounds. If bag 16 had the fakes, then you would have 137 pounds on the scale. You see you just subtract the expected weight from the actual weight, in ounces, and it reveals the bag number, regardless of working in pounds or not. It would work equally well if you added up in ounces so that one would expect 2176 ounces.

You would be in trouble if you had more bags than you had coins in each bag. Eg 50 bags each with 20 coins and thus only 20 fakes.

So what if you decided there were 8 sacks, but each sack only had 4 pieces of gold,