So I emailed SMcC and they didnt comment on the black tag at all but just said if I bought it from Farfetch, it is an authorised reseller so it will be authentic.
I personally think it looks like they have or are in the process of changing the tag colours. The bag is just too well made to be fake. The zip is exactly the same as the one on my wallet. The zip actually has a little "s" on it when you look at it from the front and a little "YKK" on the side, the same as on my wallet. Quality and weight exactly the same. The inside has a bit of smooth "leather" and its so soft, and really feels exactly like the interior leather in my wallet. The faux leather is like the softest and feels EXACTLY like real leather. I've only ever seen this on Stella McCartney items. The sandals I bought have this as the "lining" as well. I imagine its really hard and expensive to produce. Other products often feel plasticy or just bad quality. The shaggy deer is soft and feels the exact same as my wallet. The chain is diamond cut and great quality. Its sewn on really well and stiff and all perfect. It had a little plastic clasp guard too (I've seen on YouTube unboxing) and it has a farfetch tag attached. I think if this was a fake, the materials and craftsmanship would equal Stella McCartney quality and the price I paid so i'm guessing its just the real deal.
Overall, I think I was being paranoid over nothing heh. It was probably just human error in the warehouse.
I also noticed Janet, you know yours says "SP19" that's the collection it came from. Spring 2019. My number is at the top but it says "WI21" or Winter 2021.
As for whether I need/want the bag. I do need a black bag too, well one in each colour: Navy, black, silver, white, olive, burgundy so I suppose my Stella will just be my black one.
You know the weird thing, I saw this design earlier and thought it was nice and would go with how I imagine my wardrobe to look soon. Must be fate this one arrived. I actually realised the tiny bag is probably a bit too small for what I wanted, I need the mini instead. So might be a blessing I got this one and I do really LOVE it.
I will need to get a navy one in the future though (more excuses to buy another Stella haha).
I'm going to show pictures soon