Did you rent from a dealer or a rental chain(Dollar, Hertz etc etc) ?.
Many of the chains that allow you to pickup a vehicle in one location, and return it to any of their other locations within the US
My experience -
Hertz for one(may have seen Dollar do it too), has a habit of leaving a jacket or packet, hidden somewhere in the car. By packet or jacket, I mean all the loose odds & ends that are in a new car when it comes off the truck at the dealer, such as - but not limited or exclusive to :
The owners manual - a quick operating guide - service schedule - tire warranty - manufacturers warranty info(all the above often sealed & packed together) - spare keys/key code tags - the keyfob/remotes if so equipped - the
keyless entry code card when equipped - and etc etc etc.
The spare tire compartment is a place you will often find this packet stashed, if in fact their policy is to leave one hidden in the car somewhere
I guess they do this so when the vehicle is sold, there is no having to ship the vehicle packet & extra keys to wherever the vehicle ends up when it's pulled out of service to be sold.
EXAMPLE - vehicle originally put into service at a location in NY, but when it's service time is up & it's scheduled to get sent off to the auction to be sold .... it's now sitting at a rental location in SC.
Not the most advisable practice for the rental companies IMHO. Especially when you stumble across extra keys - key codes & remotes.
It is helpful tho when there's no owners manual in the glovebox & you need to figure out how to use or work a certain feature on the car. When I first discovered Hertz had a habit of this ..... I was making sure the spare - jack & all that jazz was there & I stumbled upon the packet.