I know why some pets are being shown as not being tamed by the way.
Sometimes you capture a pet and then it gets killed by an AoE spell while they're in the cage, or even by a DoT I think that's possible too. You get the pet anyway, but the cheever bugs as a result. Well, the achievement will at first display it as tamed, but then 5 minutes later you look again and the checkmark is gone and it shows as not tamed yet.
For me, no matter what my cheever was saying, if I had already tamed all the pets in the list, it would give me the cheever in the end anyway.
Which is weird though, is that when I change characters, these safari cheever do not display the same way from one character to another. The one I did on the horde side says it's not done on my alliance toons, and vice versa. But in both cases, they both are counted in your battle pet points anyway and will count normally torwards the related achievements.