Way back when I had all three splits and a bit of an over split on my right, but nothing to crow about. Flexibility wasn't my thing and had to work hard for that middle. Good thing is I didn't loose much in my older age. Still have that right, can push down that left if necessary, which isn't often unless I challenge a student, the middle is good for an old lady but not down anymore. Better than the average Jane off the street.
For those natural Gumby knees (everyone knows who Gumby is right?), I tell my gymnasts with this luck/affliction to "choke" up on the stack mat. Put the whole lower leg, calf all the way to under the knee on the mat. Big thing here is to then put your hands on the mat too and make sure your chest is up so you can really stretch that hip flexor. Putting your hands on the floor will make you lean too much over your front leg, while you might get a good hamstring stretch there, it isn't very effective if you want a leap that keeps your chest up or lay back into a ring leap/jump. Hopefully we all want a leap with our chest up right?