I have a Beseler 8021 lensboard that fits 23C / 45M / CB7 enlargers. Printed on the end flap of the box, it says "FOR ALL LEICA MOUNT LENSES Except Komuranon E and El Nikkor".

This is the board that has the little 1/4 inch diameter (roughly) plastic light pipe that shines light on the aperture scale.

I have two EL-Nikkor lenses that are mounted on plain lensboards without the light pipe. I have one of these 8021 lensboards and an El-Nikkor that needs to be mounted. I can get another plain 39mm lensboard for it, but I'm wondering what it is about this 8021 lensboard that makes it unsuitable for EL-Nikkor lenses?