The ventrals are not perfect. Ventral defects may include: uneven length, a ventral that curls or that is bent, or even lack of ventrals altogether. It is quite common for bettas to not have perfect ventrals, especially as they mature and the ventrals grow longer. I wouldn’t worry about such defects, because they are not genetically transmissible. Meaning that even if your betta has no ventrals at all (which would be your worst case scenario), it will produce normal bettas with ventrals. Many have attempted to start a strain of bettas that would have no ventrals, breeding selectively bettas with such trait, but couldn’t produce offspring of the likes. So as you see, ventrals defects are harmless.
Found this on the web.