Possibility the barrels had seen the hot salt blueing bath in the past and the solder is weakened and slowly eaten away. They will come apart in time from that and the lack of solder in the joint sounds alot like that may have been the cause. You are correct in that ringing the barrels in a worthless endeavor IMHO. I've always felt it was a nice piece of showmanship for the buying crowd but in reality it proves nothing and discloses very little. A really loose rib that would be seen upon visual inspection can sometimes be 'heard',, but don't ever expect the ceremonial knuckle wrapping it to reveal any and all flaws in a soldering job on a double.
That top lever doesn't sound right. Either it's been thinned down at some point (refinish, etc) or it's been broken and repaired midway with a poor weld or silver solder joint and that's where it's bending easily. I've seen more than a few that can be flexed downward onto the top tang so that they scratch the surface of the tang when moved, but never bent and then bent back into position like you're describing unless they were broken to begin with.
