What I was hinting at with my one word answer is that I've had both types of apparent breakdown. The sudden breakdown on relatively cheap skates, the gradual breakdown on higher end Klingbeils, where the crease didn't form for the first 10 years and 1500-2500 skating hours (an estimate), then gradually became worse and worse over hundreds of hours of skating (at least) until it no longer felt sufficiently supportive to be useable over the next couple years.
From what I've seen, people who don't compensate appropriately for obviously misfit boots can break them down a lot faster than that - and people who do triple jumps and above often dispose of them in 6 months or less. I had one coach (no big jumps) who stored her boots in her car trunk, exposed to heat and moisture, whose boots only lasted 3 or 4 months.
We've all watched people break down rental boots that were too large or weren't tied tight enough in a few minutes.
My current boots are much stiffer than I need, so I doubt they will ever break down - which has both advantages and disadvantages.
The O.P. sometimes sounds like he might have a hard science or engineering background - so I suspect he knows perfectly well that what appears to be a sudden breakdown on the outside likely occurs after an accumulation of gradual damage on the inside. Which may be why boots, at least in my experience, gradually soften over time, including the desirable "break in", a process that usually starts long before they show a clear breakdown crease.
Regarding TDL's suggestion of rebuilding boots, most or all high end boot makers will rebuild their own boots for $50 - $100 / pair, provided the breakdown creases are reasonably high up - e.g., near your ankles, rather than at the bottom, and that the stitches at the top are still in good shape. Klingbeil did it for me for free, but it would have been well worth the cost.
TDL, does Mont Clare have an advantage over using the original boot makers?