The correct nomenclature is: Short, Magazine Lee-Enfield, Mk. I. Thereafter there were several Mks, culminating with the Mk. VI.
The most common Mk. used in WWI was the SMLE, Mk III* which eliminated the long range dial sights and and the magazine cut-off.
The so-called Long Lee-Enfield was officially: the Lee-Enfield Magazine Rifle, Mk I, culminating with the Mk. I*.