Not entirely sure of the dates, but I'd like to say that the Imperial scout knives were popular in the 50's or 60's. I do not believe that they made a shell handle version of the scout knives. As a matter of fact, I believe that any official BSA scout knife, fixed or folding, had to meet certain design criteria to be able to carry the scout logo. The number one criteria was durability, IMO, cause you can imagine the potential use/abuse a scout would put his knife through.
In the 30's and 40's, and even later, utility pocket knives were the rage, and everyone was making their own version. Since certain companies had the official BSA contracts locked up, other companies got around that by copying the look of the BSA knives. The other popular thing to do was to put the word "Scout" on their knife, usually on the shield. This was perfectly legal.
I would agree that the solid handle Imperial knives (and others) of that era were "well made", cetainly more so than the shell handle knives. BTW, I find the shell handle knives have a certain charm, and while not really considered a collectible by many, I find them to be an outstanding bargain, and a great way to get into collecting.
Here's a Camco, a solid handle knife that the plastic/cell handles had shrunk up on. It was in such good shape otherwise, that I put these Maple scales on and gave it to my Dad.
Here are some other examples of the scout/utility pattern. A few are official BSA...
BTW, I am pretty sure that most of those are Imperials, maybe a Colonial or two included. There are both shell handle and solid handle, and probably run from the 40's thru the 70's.
As LT said, pics of your knives would be great.