If you're saying that editingthe DTL file on disk does not update existing drawings, yes, that is how it works. That's intentional as you wouldn't want to change, say dual dim options, which would likely be cause for a rev bump in many companies without the user's knowledge.
The contents of the DTL file on disk is read into the drawing upon creation and embedded in it when saved. If you want to apply a revised DTL file from disk, you need to do so manually.