No this is not the real lengh
I bought the rails with the help of friend that makes woodcrafting mahines.
He import rails from Italy for his macines so he accept to make an order for me too.
He told me that his provider ( of the rails ) has lengths of hiwin rails that can cut to any dimension according his customers orders.
My rails have dimensions
1840mm
1080mm
400mm
But they all have the same laser printed logo HGR20H 301 8X-5c
So it is possible that the provider of the rails cut the rails to the dimensions that i order from a piece that initialy was 3018mm.