Door Lock Function ???

[HUSSEY]

I'm trying to figure out how GM originally designed the door locks to function on AD trucks. I have a 49 with an exterior lock on the passenger side. With the door closed you can insert a key and rotate it to prevent the door lever from moving and unlocking the door.

Now, inside you can also push the door handles forward to lock the doors. I thought at first that you could push the door handle forward on the passenger side then use the key to unlock if from the outside. But I've learned that this is not the case.

With my truck I can push the handles forward and shut the door but they are now locked, with no way of unlocking them from the outside. From some research I found the following:

"Be aware that setting the inside handles to " lock " and then slamming the door , is the very quickest way to ruin your priceless door latch ~ when the truck was new , the latches were designed to unlock if you did this , now that they're all rusty and gummed up , you'll just beat the latches mercilessly if you do it....."

Is this true because mine doesn't do that? It has to be because any other way would be a pretty lame design. I'm guessing that I need to disassemble my latches, clean them up, and lubricate them. My concern is getting locked out of my truck one day by accident.

By the way my doors close and latch easily, no need to slam them.