No older proven Bowies have it. Some think that it came about as a misinterpretation of someone hearing that the Searles Bowie had an inlaid spine. That inlay is a small gold initial plate.
People that are fans of it come up with fanciful tales about them being used as a blade catcher and defector, etc..... Most that you see are modern knives from the eras after the film "The Iron Mistress" came out. That film ushered in a period of large, heavy "blinged" out Bowies that is still a popular design with collectors today.
Agree that many perceived elements of the Bowie knife is due to that movie.
Also:
Much of the relatively recent interest in this brass strip along the spine of a 'Bowie knife,' is due to a horrible abomination of a knife, which a person through the span of some years has managed to convince a lot of people (even in the knife community) was an original knife used at The Alamo last stand.
The horrible clown knife looks like the Iron Mistress on steroids and is a laughable notion, that its supposed to be original.
Several convenient clues on the knife points it in the direction of the Alamo and Bowie.
The owner had it mysteriously turn up. He then cleaned it and lo and behold, there was something scratched on the knife. Could it be ....
The owner then during the years waged a very aggressive campaign (which included threats, law suits and more, if you had the audacity to doubt the veracity of his claims) to convince the World, that his knife was the real McCoy.
Some protested whilst others buckled under for the massively waged propaganda campaign.
Some just decided that silence was the better part of valor, as they didnt cotton to the written and verbal abuse campaign.
In any event the propaganda campaign worked and word got around in broader circles. The knife ended up getting sold for an obscene amount of money (just as intended) to a misguided celebrity with more money than sense.
This much publiziced knife has a huge clip, broad blade and the aforementioned brass strip.
In part due to the above mentioned publicity in regards to this knife, brass strips are back in vogue.
There are custom versions of the above mentioned knifd made by respected makers on this very forum and yes, complete with the brass strip
The irony is that the fairy tale knife most likely will end up being displayed at The Alamo as being genuine.