Assuming you are talking about the "Pushmatic" line of breakers. I think it is the same breaker, but only thing I ever seen that one may call split bus in that line is two side by side panel sections with a common supply and two main breakers at top of each side by side section. Usually two 100 amp main breakers to come up with a 200 amp panel so to speak. You possibly could have found that they may have typically used a higher interrupting capacity for the main breakers - but I'm guessing that would be more likely today then it was at the time they were making those panels.