I have a collection of New Mini, International and Centennial Duofolds purchased on ebay from private sellers. Is there a way of recognising specifically which model they are, i.e. are the nibs white gold or platinum, is the trim silver or chrome. I am thinking that possibly this is denoted by the specific detail in the nibs. Can anyone help? I would really like to know which they are.

A nice selection, not tried the mini size yet, but have several International size and looking to get a Centennial at some point.
Try checking out the Parker pen site, link below.

http://www.parkerpen.com/en/discovery/product/duofold

All nibs are 18ct gold and on the ones with platinum trim usually Rhodium or platinum plated. The trim will either be gold plated (if it's yellow) or platinum (if it's silver). Some earlier models may have had chrome/rhodium plated trim, but I think most of the recent ones (last 6-7 years) have been platinum.

Sure somebody else can be a bit more helpful.

Andy