Nikon D810 DR at low ISO?

Hello, I've been blown away by the DR of this body. I normally try to use ISO 64 when possible but sometimes I need an even slower shutter speed and drop it to the "L.10" setting which ends up being like ISO 31. Is the DR affected technically at this setting? I can't really tell the difference personally, but just wondering if there's technically a difference?

If you can't tell the difference dont worry about it.

Whenever you go below the native ISO you're still actually shooting at the lowest native ISO. All it does is bring down the exposure in camera, like you would later in post.

That's interesting! That's probably why I can't tell the difference then.......You'd think there would be a problem with the highlights if it's just bringing down the exposure

Yes, you will lose a stop of highlight headroom. If your usual shooting style at 64 currently affords you at least 1 stop of headroom it may be useful