[Groff] Options in groff file have no effect

[nicolas . bourbaki]

Hello everybody out there using groff,

It is not long ago since I began using groff for text processing 
and I like it a lot.
After having only used the default format for my bibliography, 
I would like to adapt the output a bit more to my needs.
Therefore, I included some options between the .R1 and .R2 lines
in my example.txt file:

.R1
no-label-in-reference
.R2

I use to following command to compile the file to PDF:

grefer -S -e -p bibliography.ref example.txt | groff -me -Tpdf > output.pdf

I would expect the output to have no labels in the reference section,
however, it does.
What additional diagnostics could I use in order to figure out why the
"no-label-in-reference" option is ignored.

Kind regards,
Nicolas