I must admit, the Scarne stories are something I find extremely inspiring.
To answer the question, he wouldn't have used the Steven's cull, or at least wouldn't have known of it by the name since his apparent activities greatly pre-dated it's release.
Second, Karl Fulves apparently reveals Scarne's method in "Riffle Shuffle Methods" (there is an old thread on these forums where it was discussed). Since this book was released after the Vernon description of the Steven's cull in Riffle Shuffle Technique Volume 2, (also by Fulves) and Fulves gave the control a different name (the Scarne Shuffle Control), I can only assume that the method was in fact different.
Now back to the effect itself. First of all, there's a critical aspect of your performance, and the performance of most people's that differs from Scarne's and makes his version much more difficult, I actually only know of one other person aside from myself who has a method to achieve the effect, though that's probably my ignorance rather than a lack of other creative individuals. What you performed is a lot more like a Marlo ace cutting.
I'll explain. Not only was the deck borrowed and shuffled in the Scarne demonstration, but it was squared and a spectator was allowed to cut to any card prior to Scarne's attempt. This eliminates the possibility of jogged cards or breaks, just as the fact that, in the later demonstrations, the deck was borrowed, eliminates a lot of the possible prep-work and generally makes the feat substantially harder.
As for the effect itself. Honestly, I think it's somewhat insane to spread through the cards face up prior to, but especially during the demonstration. The reality is that, though I'm sticky about the points described above, spectators don't care. I've often done ace cutting routines using a series of false cuts and controlled shuffles, they're always very impressed, in spite of the fact that I usually start with the aces on the top of the deck, they don't know that, and the shuffles create the illusion of the deck having been shuffled. If you want to go the extra mile, which I sometimes do, but generally for cases where I'm false dealing as an apparent demonstration of culling and stacking, I do one of two things, both of which will achieve the desired effect in the mind of the spectator. The first, is to insert the cards openly, showing they are in different locations and perform a multiple shift, then simply control and reveal them. The second, is to steal them from the deck, hand it out to be shuffled, replace them, and proceed as normal. I repeat the spectators can't tell the difference and you'll end up with a strong effect.
The only time the real demonstration becomes relevent is actual cheating procedures, or personal interest.
On a related note, good job on the process, you have it looking pretty good.
If he could do this at nineteen then why did he not do this on his Castle films promo?
I could give you a number of possible reasons. First, to the average person, they couldn't tell the difference. Second, just because he could do it at 19 doesn't mean he could do it years later, some of these skills require constant practice in order to keep up. Third, there was a lot of potential material to show, you could ask "why didn't he show it" about anything he left out, and there will always be more left out than included. Personally, I'll take the word of Karl Fulves that he could actually do it exactly as he described, mind you, like I said, I know of methods of doing so and I know his supposed method was published.
I saw Jennings do the effect from a shuffled deck without controlling the Aces first. He spotted and culled them during the shuffles.
Marlo does the same in "Prime Time Marlo". There's the million dollar question though, could the deck be squared and have someone else cut to any desired card between the last shuffle and the cut to the ace? If not then it just amounts to standard culling and we all know that can be done, it's just a question of how fast and how well.
I often use the routine just to cold cut the aces from the deck then do a poker deal with the aces. I think the plot of lose the aces find them is a little strange. Why look for the aces to lose them and find them again?
Very good point, unless you made use of them in a previous effect and have them out, hence something like an insert method makes sense. That, or as a means to prove that you don't have a set up.
Which all brings up the point of just avoiding the proof and borrowing a deck that is shuffled before you get it. Frankly, to do the demonstration the way Scarne describes it is hard, possible, but hard.
And if you riffle shuffle and spot - sometimes it is hard to spot the aces. Getting 4 one after the other is no guarantee.
That depends entirely on your method, there are ways of making it work.
In performance spreading the deck and spotting solves this problem.
So does working with a set up, or one of the methods I described above, both of which I believe are more elegant from the perspective of the spectator and take less work on your part. Then again, clearly you have great success with your routine, so go with what works for you.
4 shuffle cuts and four aces is what the lay audience would expect from a magician to cut the aces. I dont know if anyone using the Stevens cull could guarantee the four aces in four cuts. To get around the length of shuffles that can happen of going five to seven and added push through. I added the cheats for the performance.
I don't know about the Steven's cull, but it can be done in 4 or less every time, though I would emphasize two points. First, that isn't the same as the Scarne demonstration, which, though perhaps not as impressive to a lay audience, keeps them more involved. Second, 5 shuffles always makes it substantially easier.
And finally, I agree with you, doing a lot of shuffles like that really isn't good for an audience. Personally my preference is to do a three segment routine that roughly mirrors that of Scarne, with competitive cutting initially.