Thanks for the great pics! It helps all Grado aficionados like myself picture how our beloved cans were built. It was really cool of Grado to let you tour their factory.
I find these pictures of interest...
The color of the wooden cups differs between each pair, some pairs being very dark. Since the cups were assumingly built and stained at or near the same time and same way, it suggests that there is variation in the wood itself that accounts for the different shades, which can't be attributed to just an aging effect as widely believed.
I'm SO tempted to make an unflattering comment about something I see in nearly all the wooden cups pictured, but I'll bite my tongue for now. Ouch! 