When I have measured my Tanner stage it was 4.3, but there was something different. From my genitals to my belly button there are no hairs or line. The area is smooth, but it seems like there are hairs on the inner thighs.
I’m not sure.
I can give your possibilities, but I am unable to give you an absolute answer.
Some people descend from a lineage that has little body hair and so any trail of hair between the groin and the belly button doesn’t exist or doesn’t grow to a noticeable extent. You would have to take note whether your father or other older males in your family have this type of body hair.
Body hair typically develops during stage 4 so it may develop later.
The order of hair development can vary. You may just be developing inner thigh hair before you develop hair on your lower stomach.
These things are not a cause of concern. It is just the set of things that makes your body unique from all other bodies.