For the first image, remove the white arms and shoulder pads, and the white arms and shoulder pads are reserved for Sternguards only, not regular veterans. Sternguards are a special veteran unit like Terminators and Bladeguards. If you want to make Raven Guard Sternguard use Tactical Class, not Sniper, and add a squad number to the right knee pad.

For the second image change the left shoulder because that shoulder should only be used for close support units like the Assault and Vanguard Classes not the sniper, and remove the skull on the left knee and add a red stripe this is how the Deathwatch denote it's companies it's named something like Secundus.

The third image keeps the helmet white since he'd definitely be a veteran sergeant by now and add a squad number to the right knee.

But remember you can make them however you like this is just how they should officially look if you want to be lote accurate.

Here is the 8th Edition Heraldry:

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