Specs is for ...
thank you for your answer.
Meanwhile I've got used to the less-than-ideal eye relief of my Nikon ED50; which means, I'll keep it. However, I've found a simple (and I think quite correct) method for measuring eye relief. The eyepiece in question has 15.5 mm - not 17.8, as specified. That explains why it's possible, but not quite comfortable to use this eyepiece with glasses.