The number of leaflets is not specific to one species or another, in each species there is a great variability in the shape of the mandibles, the size and the number of leaflets...

 in cervus 3 leaves (extremely rare) up to 6 leaves

pontbrianti between 4 (extremely rare) and 6 sheets

tetraodon it seems much more stable, at least in France originally

We have 3 distinct species which separate very easily with good criteria... as for the validity of the pentaphyllus subspecies of cervus I do not say (I still take risks but for me these are varieties or aberrations that are often found in contact with pontbrianti but not necessarily, the result of a genetic mixing still current?), I look forward to the publication of the work of Stephane Boucher who masters the subject! Analytical Tables of the Lucanids and Lamellicorns Coprophages of the Reitter Palaearctic Fauna of 1892 Miscellanea Entomologica, volume XIX, E. Barthe, Copy by Baraud in 1971. It says on page 6:

Cervus Antennal club of 5 articles; apex of the mandibles bifurcated in the male-France, Greece

Pentaphyllus Reiche -Antennal club of 5 articles, top of the mandibles simple in the male- France

Fabiani Mulsant -Antennal club of 6 articles; tip of the mandibles simple in the male- France, Pontbrianti Mulsant