Interesting, Liguy. When trying to gauge the effect of "burn-in" in the past, I would come up against a familiarity factor -- i.e., getting used to the sound of the new cable with time. In this respect, getting "better" (burn-in) could actually mean getting more "familiarised".
If (for the sake of example) "burn-in" is achieved slowly rather than in ear-catching leaps & bounds, the differences (again, assuming there are some such) would be small from one hr./day, to the next. Similarly, familiarisation may make these differences imperceptible.
I assume you've taken this into account long ago -- but your experience, being different to mine, is interesting.
Cheers!