Just 3 weeks ago, I tried to check my luggage 6 hours before my flight and was told I could not.
I have also been on a plane when a passenger deplaned and our plane was delayed while that passenger's luggage was removed.
Of course luggage doesn't always accompany a passenger --- several times my luggage comes in on the next flight --- but when a passenger deplanes, you watch and see what happens.
LoL. That is true. We can now check baggage curbside. If you remember, there was no curbside check in for baggage for 15 months after 9/11 (but what do I know). Some resourceful people found out that a person could send their baggage to the hotel in advance, contact the valet at the hotel and have pressed clothing with light starch hanging in the closet upon check-in. At the least the luggage would be in the "closet". The only point that I attempt to make is that planning can make air travel relatively hassle free.
If you are flying on American airlines to OKC through Dallas, chances are your luggage will arrive the next day! Absolute worst airline for luggage arrival with you if you had to change planes in Dallas.