Bertoia Side Chairs - Production Info  

Hi All,
I was wondering if anyone could tell me whether the production on the Knoll Bertoia chairs differed over the years and between production sites? I bought a Bertoia side chair from a seller on ebay around 5 months ago, which was manuafctured in Europe (Belguim) by Knoll.
After trying to find another white bertoia side chair to go with it for a decent price in the UK, I stumbled across another on ebay around a month ago which appeared to be an older USA production. I have since recieved the chair and put the two together and they appear to differ slightly in overall dimensions. Particulary the seat height seems to be slightly lower on the european manufactured chair. When purchasing them I looked for all the tell-tell signs to ensure they were authentic and I dont believe either are fake. Any help or advice would be greatly appreciated.
Thanks