Erik Kripke had initially intended to have Sam & Dean drive a ‘65 Mustang but went with the ‘67 Impala because his neighbor said you couldn't fit a body in the trunk of a Mustang, you would need a car like an Impala.
It does not say Federal Bureau of Investigation on Sam and Dean’s FBI badges. That’s because even if it’s just being made for a prop on a TV show, it is illegal to make a fake FBI badge. Instead they read: The Federal Bureau of Justice, United States Department of Investigation.
Sam and Dean were originally supposed to find their dad on the very first episode burning dead on the ceiling, but this was later changed to Jess.
Eric Kripke’s original idea for what would become Supernatural was a show following a pair of reporters going to investigate urban legends and writing about them in their newspaper column, and was going to be called Unnatural.
The writers wanted Sam and Ruby to get married, but once Jared and Gen got married in real life, they thought it would be tacky to recreate it on the show…
Sam’s name was originally going to be Sal, but they thought it didn’t sound right and changed it to Sam. The Winchester’s last name was originally going to be Harrison to pay tribute to actor Harrison Ford (because he wanted Dean to have the “devil-may-care swagger of Han Solo”). At some point it was changed due to someone named Sam Harrison living in Kansas, and had to changed it for legal reasons. Winchester was picked because Kripke likes the Winchester mystery house (Originally owned by the gun manufacturer, now a famous haunted house). John was going to be named Jack, but again they found there was a person living in Kansas with that name and had to change it.
So thanks to those people in Kansans we don’t have The Harrisons saving people and hunting things, because can you imagine Jack, Sal and Dean Harrison??? I’m not even going to get into the fact that Jensen was originally going to play Sam but liked Dean better…then we would have Jensen playing Sal married to Ruby and…
Just thank Chuck we ended up with Jensen as Dean and Jared as Sam and their last name is Winchester NOT freaking Harrison, and they are not reporters on a show called Unnatural.
I’m not sure what sources you’re using but some of these are rumors.
Jared and Gen didn’t announce their engagement until January 2010, nearly a year after they filmed Ruby’s death. The writers couldn’t have scrapped a Sam/Ruby wedding idea due to Jared and Gen getting married because they didn’t even get engaged until long after Ruby’s final episode was written. (x, x)
Jensen originally auditioned for Sam but was not offered the role, nor did he ask to be Dean. The producers called Jensen and asked if he’d be interested in playing Dean (because they’d decided to go with Jared as Sam), Jensen said yes and that the role had interested him from the start because he thought Dean was funny. (x)
John dying on the ceiling instead of Jess was one of many ideas that were scrapped and revised while writing the pilot but it wasn’t the original idea. The teaser Kripke wrote had John dying when the boys were young but he decided it’d be more interesting if they were raised to be hunters. (x)
The rest is all true.