When dual cylinders are used - one for each shoe, performance is increased. Trailing shoes, on single cylinder systems, just don't do much. Its the leading shoe, that tends to bite into the drum, aided by the direction of rotation, that does most of the work. Noting that: some single cylinder systems on vehicles will use two different types of lining. A softer grade for the trailing shoe, so it will bite into the drum better, so it will match the work of the front shoe. Another example is the M37. The single/double acting cylinder, has two different bore sizes. The larger bore goes to the trailing shoe, giving more force to make it bite in and do more work. Hence it very important to get them installed correctly.
The later trailers are just using a more efficient system by using dual cylinders/one for each shoe! When I grew up using single system brake systems on vehicles, we didn't know they were dangerous and that we needed dual brake systems. Some how, we managed!
Lee in Alaska