You can also "qualify" for a blue card numerous times within one membership and transfer the benefits via gratuitous transfer. There is not "one blue card." It's the contracts, when they were purchased, the number of points on them, and how they were acquired.
For example, someone could have purchased a 25 point
DVC contract resale prior to 2016. Then in 2019 added 75 points direct at CCV. In 2023 VGF direct was tempting so they added another 150 points direct. Say this person has 2 children. The owner can do a gratuitous transfer of the 75 CCV points to one child and the 150 VGF contracts to another child. In this scenario the original owner and both children will each have their own membership with a blue card. This is because prior to 2016 resale contracts got blue cards. As of 2019, 75 was the minimum direct required in order to get a blue card. In 2023, 150 was the minimum direct required in order to get a blue card. The contracts are minted at time of purchase. If resold now they become resale contracts and lose benefits. If it's a gratuitous transfer the contracts keep the same blue card eligibility at original time of purchase.
If someone joined today by purchasing a 100 point and 50 point contract they would have a blue card. If they did a gratuitous transfer of one contract to a child both the original owner and child would lose the blue card because neither are meeting the required number of direct points at original time of purchase. Both owners would now need to acquire the additional required points at current time of transfer to receive the blue card if they still want it. If transferred today the 100 point owner would need 50 more points and the 50 point owner would need 100 more points. If in five years the minimum is 300 that becomes 200 more points for the 100 point owner and 250 points for the 50 point owner.