I am currently using a library that is licensed under MIT.
Each file of the library has a in-line comment containing the standard MIT license text in full length, which is kind of repetitive in my opinion.
So my question is, can I remove the in-line MIT license and replace it with a notice like this:
This file is Licensed under the MIT License see /Project/lib/MaterialDesign/LICENSE.md
in the root folder of the library?
When using longer licenses like GPL and Apache it is common to point to a full copy of the license but the shorter ones like BSD or MIT are normally kept whole. There are no strict rules on where you place the full license info, it is just common to place short licenses in full and longer ones as a reference.
You can see that this question hints that not all projects copy the MIT into each file.
There are some practical reasons against doing it:
If someone took single files out and moved them somewhere else it would be more convenient for them if the full MIT license was kept, so he/she would not need to copy it in-line again. Leaving the information directly with each source file is less fragile. And even though it is kind of repetitive, modern IDEs usually show the copyright notes in a collapsed form. Using the proposed note, may mean additional work for the user (needing to check the content of that LICENSE file, just to be sure that it's really MIT).
Now the legal stuff:
I have seen many projects where there is a copyright information only in the license/readme part and not with every source file and they seem to be doing just fine. For a better discussion, see Do you have to include a license notice with every source file?. If there is no duty to add license information to each source code file under MIT (and nothing in the MIT seems to suggest otherwise), then your proposed notice is fine.
