@sardak double lines
As far as i can see your tail close up photo has 3 vertical lines. If you look closely they appear to be double ones. Not as clear as on the 'groove' picture, but still.
What strikes me is that these lines cross from leading edge over to the centerbox. These are respectively GFRP and CFRP built up components.
So it is rather unlikely that the origin of these stripes had anything to do with the lay up of the various composite layers.
This could suggest that it originates in the painting scheme ... which usually includes both spray paint and very large plastic decals (read: stickers). Would be interesting to find out how they did the change of livery. Did they just stick large decals with Metrojet over the old ones or paint ... and perhaps sprayed a coating over that.
I do not know, but this may be part of an explanation.
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Take a look at the white leading edge ... borderline does not look very sharp ...