Whether the trades are independent or dependent depends on the method and the time scale. Anyway, it's easy enough to calculate the probability of a win, following a win, vs. following a loss, and answer your own question...
Ever heard of adding to your position if the trade goes the right way? There area plenty of studies that show trend following systems benefit from adding to your position. If the trades were independent that wouldn't be the case, for this system.
Better yet, if signal A ends up working, what's the probability the next signal B will work, as opposed to the probability of all signal B's?
One thing I found was the famous three bar pivot breakout method (signal B) has a significantly greater probability of success on a gap day (signal A). This was on the entire March 03 NQ contract.
Statistically independent trades means there is no "bigger picture" to view the method against. Put another way, things we don't understand appear random.