There is a big quality control issue with uploading designs onto individual products that need to be addressed at some point, MerchByAmazon.
As it is now, an uploaded design for t-tshirts gets assigned to all these products: Regular T-shirt, Premium, V-neck, TankTop, Long Sleeve, Raglans, Sweatshirts, and Hoodie backs.
The quality control problem is this: The design is placed and sized differently on some of those products. Specifically V-necks, Men's Tanktops, Women's Tanktops, and Raglans.
I have to create separate files and separate listings for each of those products if I want the best possible design placement and sizing.
The best example of this is Tanktops. The design on tank tops is printed on a smaller area than the t-shirts. I have to resize the design and make it larger so it looks better on the tanktops. Then the men's layout is very close to the neckline and women's is further down, so I have to create 2 individual files with the correct placement for both men and women separately, and then upload them under 2 different listings if I want the best placement of the design that is pleasing to the eye and how it's worn on the body.
I've written about this before both in the forum and directly via email, and I hope at one point it can be addressed.
Maybe this is being addressed in the new update that focuses on design submission count rather than product submission count? I would hope. If you need inspiration, think about how Red Bubble operates for their design submission. Each individual product can have a unique file assigned to it that is sized appropriately. Perhaps the Merch team never really considered how this could affect the overall quality and ease of design management for their creators. I would like to be able to keep one design under the same listing, and not create separate listings just to go for the best layout and sizing on individual products. That defeats the purpose of having the multi-uploader tool.