Or that the lenses haven't been opened for cleaning in a while, or the lubricant has migrated to the blades...
Not all lubricants sublimate in such a way to redeposit on glass and have an optical effect. I had a Nikkor f/2 85mm that had oil on the blades, and yet produced fine images with great detail, without flare or haze around specular highlights.
My Jupiters have it. Most of 'em anyway, and they too take very nice pictures.
I think my Summicron had oil on the blades but I don't remember.
Oil on the blades only bother me for SLR use, where sticky blades slow the aperture's rush toward what I preset.