Shortly after my original post, I did find this video, which discusses some details of how the bag attaches to the frame:
https://www.youtube.com/watch?v=FrHANXcJ5rsPlease correct me if I'm wrong, but it looks like Evo/Revo bags have a ladder lock sewn on the lower sides of the bag through which webbing, attached to the lower sides of the frame, weave through. Those ladder locks allow the bottom of the pack to be cinched against the frame or extended away to expose the load shelf.
Bags also have two pairs of webbing sewn to the upper sides of the bag. Only one pair is used, depending on the height of the frame. The webbing goes through a tri-glide attached to the upper frame encasement (it's this encasement that moves up with the addition of frame extensions) and then buckles are attached to the loose ends of the webbing and allow the two ends to be joined together and tightened to draw the bag against the frame or loosened to allow the bag to fall away from the frame. Is there enough webbing length for the buckles to remain connected when the bag is fully-extended from the frame?
Beyond providing a place for a spare set of buckles and a grab handle, what is the reason for using the tri-glides and buckles for the upper bag attachment vs ladder locks for the lower bag attachment? Would ladder locks have been prone to slipping with the increased tension/leverage that I think exists on the upper bag webbing when there is a heavy load?
If the above is accurate for the Evo frame, is it also the same for the Revo frame? The bottom frame webbing and upper tri-glides should be roughly the same distance apart as the bag's ladder locks and upper webbing, but I can see how some variability can still work. Kevin, is this variability what you're referring to when you say that some of the Evo/Revo packs may interchange on frames, but not necessarily fit/work as well as on their proper respective frames?
Furthermore, did the distance between the harness locks on the upper encasement and the harness mounts behind the back padding increase in Revo compared to the Evo for a given frame height? Is this the reason why it's been mentioned that the webbing on an Evo harnesses may need lengthening to work on a Revo panel?
Sorry if these questions seem nit-picky. I'm not trying to be critical --- I'm just really is interested in how the pack works and trying to understand the implications of my purchase of the Evo frame vs the upgraded Revo frame.