For my twins, Sportfan, it never did correct itself. I tried caking the girls up one right after the other at the same party and they still ended up with different next-birthdays. I just left it that way. While not realistic, it did make coordinating their birthday celebrations easier when I had a break between.
They also had vastly different zodiac signs. If it was real life, their signs would have been nearly 8 months apart
.