Are you working on the front channel or the rear channel for a front door??
The original discussion was concerning the front channel.
The rear channel of a front door does have a separate lower section that can be removed/replaced.
Looks like that channel is missing. Not sure how that would be fixed
without the channel which someone with skills could try to tack weld it back in place if you had the part. That channel likely was installed while the door was being built but before the outer sheet metal was attached. WAG...
OK, I re-read the original posts and looked closer at the photos:
The metal channel (for the rubber glass run) is either missing or out of place for the front left door.
Normally for the front doors the front channel (for the rubber glass run) should be immediately behind the front speaker...