Hi! Yep, this is a newer model, from the Fall Winter 2017 collection, the color is called Lapis. Now, it's most likely authentic, but clear pictures of the logo and the other side of the label where the logo is printed would be necessary to for us to be sure.
Bear in mind that it's a Tiny, not a Medium, so it's a bit smaller than the bag you already have. But I think it's priced quite reasonably, so I totally understand the temptation!

Also, it's not a PS1, but a PS1+ - you can tell them apart by the front flap. On the PS1+ it's one-piece with some decorative stitching. The PS1+ was a sort of "updated" version, not replacing the PS1.
https://www.fwrd.com/product-proenza-schouler-tiny-ps1-in-lapis/PROE-WY282/ Here are more pictures and dimentions.