This follows from yesterday's post, and the comments on it. I had intended to make this a comment, which is maybe all it merits, but realised that no-one might read it if I did.
The suggestion was made that the figures "laid down" after a volley are not simply killed and wounded, but represent the number who are no longer available to fight back, for whatever reason, and that morale-type considerations will be a large part of this. I'm not talking about Charge! here, but I may well be talking about games of the same general style (and vintage?) as Charge! - if the "casualty" figures are really the overall reduction in combat effectiveness, as discussed, then they represent a nice get-out for those of us who find separate morale testing a tedious overhead.
Further - and this is where we get to this morning's wacky idea - this implies that your Old Guard should be harder to "kill". If they can fight on longer than lesser beings, then the proportional fall-off in CE should be slower in the same situation. It is a commonplace to allow good quality troops to shoot/fight better, and give them an extra dice (or something), but I do not recall ever seeing rules which gave an extra firing dice because the target unit were shaky. Maybe I should have? It would work, I think.