St Dupont Identification

[FabianoMarijuana]

Hi, recently I bought a st. dupont online and I would greatly appreciate on identifying the pen and the authenticity. The pen looks like a classique although I can't find one with this exact model, I only found this pattern with a silver plating. The code on the cap spells "57REB30" and the made in france tag is spelt on the other end of the clip instead of under it. My main suspicion comes from the fact that the nib feels a bit dry and scratchy. Help would be greatly appreciated.