In this area as well there is, perhaps sadly, more research into American Sign Language (ASL) than the Sign Language of the Netherlands (NGT).
But what we do know, is that signs can change shape.
So for example, a sign that is made with two hands, and both hands have...
...different hand shapes, like this for example, has the tendency to change into a sign with two similar hand shapes.
That's been described as having happened in ASL, and it probably also happened in NGT.
So there's what you might call lexical change.
Technological developments have also played their part, of course.
Just consider the sign for telephone. Perhaps it used to be like this.
And later it became this, and by now it's become this.
So this is another case of motivated lexical change.
And if we take age differences into account, education obviously is important.
Older deaf people have often received different education, which can also play a part.
Like, how often do you use your mouth when signing, how often do you use fingerspelling.
Here we can see clear differences between generations.