Chanel Eyeshadow Duo, autentic or replica comparison...confused!

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I am a super busy mom so most of the time I do my shopping online. I've purchased chanel eyeshadow duo number 81 a year ago. Since the bottom is showing up I decided to purchase a new one with the same color because that's the only color I can wear on my daily job. Very light and calm colors perfect for daytime and fits our uniform. I wonder how come it is cheaper than the one I've purchased before. The old one is 6g, if not mistaken, it worth around $55 to $58. The one I have now is 1.2g comes with the same price.They have the same price but differ in grams??? Mostly less contents less the price, am I right? But still I ordered it. Now I have the new one already on hand. They have the same maker and same packaging. A little difference in pigmentation although I'm not much particular with that. As long as it is wearable and lasting. So far I don't have the allergic reaction yet if it is really a replica or not. My concern is do brand cosmetics really have replica? Just curious so next time I should be careful purchasing online.