H6 boots always split at similar times because of the exhaust locations they get even wear.
h4 normally wears more on the drivers side because of the exhaust running down that side only.
We had a customer today with a H6, he was certain we had only just replaced the inner cv boot 3 weeks ago. I told him he was correct, because we had, on the drivers side. I also mentioned to him that his cv boot was now split, on the passengers side, because he ignored our recommendation of fixing them both at once. The previously unsplit boot (which showed signs of perishing and dryness) was now split and needed replacing, and it took me ages to get him to understand that it was a different part we were now replacing.
oh well, you live and you learn

Built not bought, it's a way of life.