The smell comes from the tanning oils and any other chemicals that are used in the production of the leather. If the leather is different, then the bag has a different smell. For example, I find the smell of the Dior Gaucho from the Galliano era quite different from the other Dior bags of that time. The washing and waxing of the Gaucho leather gave it a very distinctive smell.
On top of that, boutiques are scented with a unique house fragrance (most luxury brands have their own boutique scent), and sometimes that scent lingers for a while on their products.
Thank-you so much for sharing your prescious information!
I fully agree on the Gaucho bags- they are the most delicious! I am very happy to own three of them (a huge black one, a medium black and a medium red) and each time one comes out of its dust bag it fills the room with a scent of pure joy no matter whether it is cold or warm!
The last Dior bag I bought is a rather battered big Karenina. When it arrived on a very cold day it did not have any scent, but after warming up it started to give off this joyful Dior leather scent, too. Even my 9-year old son noticed it and complained when I took the bag out of the room.
I really wished Dior would make it into a perfume!