This keeps coming up

I took three 8 week old kittens to the vet today. They kept insisting & even wrote down in their paperwork that the kittens were 6 weeks old. (Incisors have not come in yet) -they noted. 
They thought I was lying to them. 
 I was present on Christmas Day when these kittens were born, and have kept a log book as they age. so I know for a fact that they are 8 weeks old. You may have seen them on my website or watched them on YouTube.
Here's why this worried me... what if a customer took a kitten that they adopted from me, to their vet, and the vet tells them... "Well, hunny, that lady lied to you. Because these kittens are only 6 weeks old."
Last year I had a customer come back and accuse me of lying about her kittens age. She said that her vet told her the kitten's REAL age, and she believes him over me because he is more educated. I got so mad that I went and made a video about it. 
https://youtu.be/Lbt37qTM4Yw?si=ldBG1VyiNZHjg-D2