The spring counts apply to oem springs. Aftermarket springs have always been available but may have differences.
The characteristics are the only way to be able to more closely ID spring packs. Width, shape of tips, and leaf thicknesses can help. Folks repaired things more back in the day. If a leaf cracked or broke, owners might find the next closest piece that they could get to fit. It's good when a pack still has uniformity in thickness, shape, and receding lengths of leaves. I've seen all sorts of botch jobs on springs just to keep the vehicle in service. This came from growing up in the dust bowl region of the high plains where few roads were paved and many were no better than a cow trail in a pasture.