Eames pscc-4 chair details  

I can't help, but I'm curious about those extra screws going through the bottom, presumably holding the seat cushion in place. Are there also screws holding the back cushion in place?

Great find! Congratulations!
The extra holes in the bottom are indeed interesting. Especially since the screws seem to the same as the ones in the base. (that would mean they are original to the chair)
The bumber edge is also quite interesting, Normally you would find these on totally upholstered chairs. So that could mean that your chair was originally fully upholstered. However, the rim seems to be well fitting to the edge of the chair. Perhaps it was added to your chair to give it an extra protection.
Judging on the mark, the cushions and the overal look, I think your chair is probably end 1970's.
Again, a great find!

Those screws look like 1/4-20 machine screws, most likely going into threaded inserts in the upholstery.
A quick google image search reveals that other examples also have the screws. The search also reveals an example with the black trim around the perimeter.
http://www.artnet.com/artists/charles-and-ray-eames/pscc-4-rrlJOaWFGKS3q...

Those screws on the back seem like a pretty inelegant way to attach a cushion. Would adhesive not be strong enough for this sort of application?