Different machines and modules have different maximum values for trainings. For example, terrarium with tentacles can penetrate women in 3 different ways, but never gets their skill in these above 50. (but if they are already trained to like that, you can get a lot of positive emotions in terrarium)
And yes, for many skills, we can't get the skill above 100 with machines we currently have.
Encrypted data is a trait that can be seen when examining a sample's traits. If there is no such trait - you can't extract the encrypted data.
And yes, when extracted, it seems to only be good for selling. With terrarium's cheap training prices, it's usually worth the resources, but not necessarily worth the player's effort.