You have neither answered nor addressed the question I asked. I never asserted progression is supposed to be linear or unbounded; I was doubtful as to whether my progression strategy was reasonable and optimal and asked for people's views and justifications on what they think constitutes a more reasonable and optimal progression strategy and cases for deviation; a legitimate and pragmatic question in brain training as well as general learning and as far as I've been able to see in this forum has neither been asked nor answered adequately (it's not the same as asking "how do I progress past 3,4,5,etc. back?"). I also never made any claims about IQ so it's asinine to address such an absurd contingency rather than the question. My interest in Dual n-back is to improve WM regardless of whether it yields a direct increase in IQ (I'll even go as far as saying I believe studying math and philosophy are more likely to yield increases IQ than any brain training game)
I would also point your claim "there is no successful or non-successful brain training strategy" is self-contradictory and flies in the face of evidence. Empirical evidence has shown that certain tasks do not provide any reasonable expectation of "far transfer" and are therefore non-successful brain strategies (e.g. playing Chess does not to appear to have significant far transfer effects). Conversely, increases in skills such as mathematical and verbal ability have reasonably strong correlates with IQ (even most of the rules that show up in a typical "culture-fair" test like Raven Matrices test are easily recognizable set theoretic, geometric, and logic procedures), suggesting that using those domains for brain training are likely more promising for far transfer effects than Chess and even Dual n-back (a view somewhat supported by the observation that each year of compulsory schooling correlates to a 1 to 5 point increase in IQ per year) and therefore are examples of a possibly successful brain training strategy.
Additionally it is trivially clear both logically and empirically that
certain progression strategies are better than others. For example,
picking an n-back that's easy and doing it for a year before increasing the
difficulty is clearly a horribly inefficient progression strategy (at least in relation to mine). Furthermore it is possible that perhaps requiring a faster time per stimulus (say 2 seconds/trial) at n back before progression to n+1 back may be more optimal than my own strategy (which allows progression at 3 seconds/trial), though it is not clear to me if that should be the case as one could argue they can improve working memory speed before advancing, but another may counter saying they can develop speed at n+1 back anyways and avoid unnecessarily easy sessions (and it is particularly that type of discussion I was seeking to elicit and understand when making this post).
It would be prudent to ensure you properly read and understand the question before answering.