I am curious as to whoch libertarians are you referring to.
We use defintions consistent in form and time. In fact our vocabulary and positions pretty much haven't changed for 150 years. (possibly aside from the creation of anarcho-capitalism, which however still uses the same definitions and most of the positions, it just goes a bit further with them.)
Most often we are criticized for not pushing the overton window (usually verbalized as "not going with the times") and using overly abstract definitions (the exact opposite of what you are accusing us of) instead of the modern ones. (the ones that are modified to fit the current dominant natrative)
You can for instance read Frédéric Bastiat's work and find, that he uses pretty much the same defintions I do and has pretty much the same talking points despite being born over 200 years ago. Almost no political school of thought can say the same.
So once again, I am curious as to how did you figure what you are accusing us of? I am genuinely curious.