I have only had 2 for 5 years, but I can just glance at them and know who's who. I don't really look at pattern, I just know...

But if I did have to look, my girl is much darker than my boy. My boy also has a big scar from a feeding accident on his neck (lol, his neck.. how does that exactly work??) I never really used pattern in the begginning to tell them apart.