Why was this lined changed in No Country for Old Men?

Question

In the opening scene of No Country For Old Men (2007), Tommy Lee Jones's character, Sheriff Bell, gives a voice over monologue in which he mentions sending a boy to the electric chair in Huntsville, TX.

I noticed that this line is almost exactly the same in the book except for one difference. In the book he sends the boy to the gas-chamber. It is also the opening lines of the book.

Ok so its different... big deal right? But I looked at several versions online that I could find of the original screenplay and in the Coen Brothers' original script it is the same as the book, referring to the gas chamber, not the electric chair.

So I did a little historical research about Huntsville, TX death row and the history of capital punishment in Texas and found the following facts:

• Hanging was means of execution between 1819 and 1923.
• The State of Texas authorized the use of the electric chair in 1923, and ordered all executions to be carried out by the State in Huntsville.
• The State of Texas executed the last offender by electrocution on July 30, 1964.
• Due to Supreme Court decision in 1972, execution was declared "cruel and unusual punishment" and death row was cleared by 1973.
• The State of Texas adopted lethal injection as means of execution in 1977.
• The State of Texas executed the first offender by lethal injection on December 7, 1982.
• No executions apparently occurred between 1964 and 1982.

Given these facts, it seems historically unlikely for Bell to have been able to send anyone to the electric chair. For this to be true it would have to have occurred in 1964 or earlier. If Bell was 25 when he first became sheriff then that means he was born in 1939 or earlier and is at least 68 in 2007 (and almost 10 years older than Jones himself was at the time of shooting the film). Not saying it is impossible, but just seems very highly unlikely to me.

So my point is, why was the line changed which was spoken by Jones in the film?

Actual line from movie:

Bell: There's this boy I sent to the electric chair at Huntsville here a while back. My arrest and my testimony.

Excerpt from the book:

I SENT ONE BOY to the gaschamber at Huntsville. One and only one. My arrest and my testimony.

Version from original script:

BELL VOICE OVER: I always liked to hear about the old-timers. Never missed a chance to do so. Nigger Hoskins over in Bastrop County knowed everbody's phone number off by heart. You can't help but compare yourself against the old-timers. Can't help but wonder how they would've operated these times. There was this boy I sent to the gas chamber at Huntsville here a while back. My arrest and my testimony. He killed a fourteen-year-old girl. Papers said it was a crime of passion but he told me there wasn't any passion to it.

Answer 1

I have no proof here, just a sense of appropriateness.

"Gas chamber" is an obviously emotive term, one which most modern studios would wish to avoid as it's not palatable to movie audiences.

People are more used to hearing about prisoners being sent to the electric chair than being gassed, so it seems a reasonable substitution both in terms of audience expectation and sensitivities.

I'm guessing that if "gas chamber" was in the original script, someone must have said something, or there was a negative reaction raised and it was subsequently changed.

As noted in comments, it's unknown whether the actor, writers, directors, or the studio (or a combination of them) mandated that change to the script.