Page 135 - "An edge is nothing more than an indication of a higher probability of one thing happening over another." (thanks wareco)
If you agree with the above statement, then I would say over a series of trades you would have a positive expectancy.
How many trades would it take for someone to feel confident in there edge, it would be different for every trader.
Having said that, I lean more towards the ready, fire, aim, school of thought. I need to immerse myself in whatever I am doing. Its to easy to get all intellectual about something and then base your assumption on a thought and keep going down this road of assumptions and thoughts about how you would like it to be.
In other words you can estimate that it will only take 3 hours to dig that ditch but until you get down to the actual process of doing it and running into roots or a waterline or whatever is beneath the surface it's all just an interesting mental exercise.
Its kind of like swimming you could read a 100 books on the subject but until you got in the water and started flailing about then and only then can you start to apply some of the techniques you learned in the books.
Now if you are a super trader and have already mastered yourself and can control your emotions and execute your edge as written then you already have your answer.
Its similiar to starting a new business you have an idea, you don't know if it is going to be profitable, you have to try it out, take it for a drive, see how it feels to you. It has to align with how you see the markets.
I went back and read your question again and I think I kind of veered off the road a bit. That will teach not to reply to a thread while I am sober.