The analytical mind isn't binary. It's not on vs. off, but more a matter of degrees. Sometimes the mind, regardless of listening mode, has a clearly formed opinion and other times things are kind of opaque. All of which leads me to believe that most "upgrades" are subtle.
If it takes you months to make an evaluation, then I think it's just as much a reflection of your mind and body's movement over time than the actual change in your system. Your weight, blood pressure, eating habits, sleep patterns, sexual activity, exercise, drug usage (both medicinal and recreational), illness, etc. all have a direct bearing upon what you think and how you feel about the sound of music.
Does the system change make a difference? Do you like the difference? The words of the poet illuminate:
First there is a mountain, then there is no mountain, then there is.