Hi all. I am going through something similar and wanted to share my experience. I found my Sac de Jour in 2017 and it is one of the original 2013 models. I love it, and hardly wore it. However, as they are known to do, it had started to lose its shape.
Being a beautiful navy smooth leather, and since I did not originally buy it, I understood that YSL would not restore it for me. So I took it to 'Lovin My Bags', who had done quite a lot of cleaning and fixing of other items for us previously, and till now, good work.
Upon seeing its 'restoration', while the structure was back, I simply didn't recognize the bag. The color was muted, and the bag was matte. It was also glittery all over with some kind of metallic spray. We thought it must be someone elses bag!
Apparently, that is now fixed. However, there are now considerable wrinkles in the handles, near where they meet the attachments. Apparently, that is somehow to do with 'reinforcements' and is not now fixable. (photos attached) I am yet to pick it up and am asking them if they can do something. Apparently, the wrinkles go when you lift it (before it never had such an issue at all). I guess I will never place it on a table again, then!

haha!
I really have no idea what they have done to this bag, but it's clearly far too much. I just wish YSL would let you pay for repairs as long as it's a genuine item.
Here are the photos. It took me over two years of other work to even trust them with this bag!
1: prior to work - you can see the bag needs some structural help, or 'restoration' which is what I requested and cleaning to remove grease etc, as required.
2. Full "restoration" : (you can see some wrinkles here too)

3. "Fixed" color showing wrinkled handles looking worse:

4. Close up of the wrinkles.
The color does look better, at least in the photos... but if they can't fix the handles, I think I may regret it now!