I use Civil 3D more than other software. I believe this is and AutoCAD feature though, but there is no AutoCAD Idea forum that I can find.
I have worked with many companies in my years of consulting. I have always run into an issue when talking to users who have custom linetypes and I ask, "From which file is the linetype coming from?" Users look at me and say they don't know. So I post this. . .