Arne Jacobsen Series 7 padded chairs! - date?  

Speaking from an upholsterer's point of view, there are certain styles of furniture where decorative nailheads are appropriate and original.  There are many, many other instances where they were added later, often because a DIY'er or a hack "professional" could not figure out the correct way to fasten down an edge of fabric, or because someone just loved the look of them and had no sense of whether they were appropriate or not.  I think people often make changes like this so that the piece will fit in with other stuff in the room.
That's why I would assume these aren't original. That and I've never seen them on any Danish furniture that I can recall, and that the nailheads and the poufy padding seem very much opposite to what this chair design is about, which is a very pared-down, simple look.  And that the chair was available in an upholstered version that was a minimally upholstered as possible.
I agree with those above who suggested that you ask if there's someone at FH who is familiar with the history of the designs.  I'm sure that there is someone there who would know about such things.

Hi folks! I'm both relieved and disappointed to report that I've heard back from another FH person, who confirms your various unanimous views :-):
The chairs are original Fritz Hansen, but the upholstery with the buttons has not been done by us. This seems to have been added later on. 
 
The ones where it says 0164 or similar numbers: They can be translated to January (01) 1964 (64)
 
The chair without a central screw are most probably made between 1955 and 1963.
 
Let me know if you have further questions.
 
Best regards,
Philip Grütter 

 
Philip Frédéric Grütter
Sales Coordinator

We have a set of these in my old University office. The building was opened in 1976, they are Fritz Hansen and the chairs have no nailheads (and look much better for it)