Placement of numerical references (“[1]”) I kind of struggle with my students. I always told them to put the reference number (identification) close to the cited object - to make really clear what is the cited object. For example:


The theorem:


  Theorem A [1] is great ...

The study:


  In the study [1] it is possible to see that ...

The statement:


  It was proven that usage of ... leads to problems [1].



However, my students keep doing something like this:


Citation is related to the previous sentence! (probably):


  ... and it was proven. [1] The general idea ...

As above, but with extra period:


  ... and it was proven. [1]. The general idea ...

After the entire paragraph:


  ... and it was proven. [1]



They are arguing that this referencing is correct according to the ISO norm/suggestions. They keep doing that even though I told them to not do so. And they generally try to comply with my guidelines. This is a real exception. It seems this referencing idea is deeply rooted in their brains.

My questions:


Is their way of referencing legal? If yes, where are informations how to read this fuzzy notation? And why it does not appear in top journals?
How to tell them that this referencing is really unclear in a way that they will understand.


Note: The students I am struggling with are from all continents/countries, pursuing a university degree in electrical/software/mechanical engineering. I would say they are mostly 22±2 years old.
The universities with which I am familiar decide at the faculty/school/department level which referencing style will be used in courses that they teach/manage. This means that:   


a standard referencing format is set across all courses and classes within that area
students do not have to struggle with different formats within the same subject
referencing guides with comprehensive examples are readily available for the stipulated referencing format
there is no need to argue/justify/negotiate with variations


If this is not the case, choose a popular referencing format (Vancouver style uses numbered citations) and apply that. Give the students a link to a Vancouver style guide such as this, as well as handing out a printed copy at the beginning of the semester.

When/if they then argue that their referencing is correct it can be compared to the established style guide.

To be truly effective (in changing habits) the referencing needs to be included in the assessment rubric.