Bernard has provided a great explanation.
I read your question, and just add a few inputs:
1) 16/1860 with the 3.96 calibre &
2) 16/1860/2 with the 1.96 calibre.
a) The calibres are of not in limited edition, it is the model ie. the 16/1860/2 with various casing (WG,RG & PT) and dial configuration.
The 1.96 calibre is used in another model - the TWIST 16/1888.
b) To differentiate the 16/1860 & 16/1860/2 besides checking the calibres ( from the open case back), the dial spots the following difference:
i) Decor flamme guilloche for 16/1860/2
ii) 16/1860's dial not guilloche. Below the Chopard logo,printed 'Geneve Depuis 1860' and at the 6'o clock there is a round index.
The LUC finishing is superb. You have to see it for yourself.