Well I don't know about all of this.

I agree if you use the same razor all the time or maybe alternate between two or so as the edge starts to dull you won't notice it and its really amazing how you do get used to it and its only if you switch to a "sharp" razor that you realize. I found that out years ago when I was doing "the grand experiment" and I was using the same 3 razorss day in and day out. Every so often I would switch to a fourth I knew was sharp so I could gauge how the others were deteriorating.

Otherwise with me I have a daily rotation with about 30 razors so as soon as 1 deteriorates the slightest amount I'm very much aware of it. I have a few I have been using for well over a year, some for years now and have not had to even touch up once but in general about 15 -20 shaves and the comfort factor starts to go even though it still gives a bbs shave and for me a few trips on the coticule or escher and its as good as new(or shave ready which is better than new actually)