This is one of the example of my own. Few years Back, I have UE Triple.fi 10 pro I bought it when it first come out. My friend bought it a year later. So after he bought it for 3 months, I took 2 earphone for test. Using the same player and play the same songs, I definitely heard different sound of this 2 earphone. Mine have better sound than my friend and my friend also agreed.
From this I know some headphone or earphone need runin time, but some may not. Also some need take much longer runin time than the others, So it all depends on which headphone or earphone to choose. For me, I still enjoy every minutes of a new earphone. I enjoy hear the sound change when time move on and enjoy the music you hear. Enjoy!