Anyone who registered with Spreadshirt after October 19th, 2016 is using the Partner Area. If you registered before this date, your account still runs on the old technology. This is what the differences look like:
Legacy User Area
Because this requires all our attention - and because the technologies of the two versions are so different - we have not actively developed the Legacy User Area for years. This also results in different functionalities: Some features are only available in the Legacy User Area, while others are only in the current partner area.
Bugs that affect the central process of uploading, creating products and selling will be fixed in the Legacy User Area. Moreover, the Legacy User Area is no longer supported (e.g. by bugfixes) and new features are only developed in the (current) Partner Area.
In software development, this is a common way of realizing ideas. It helps us equip as many Partners as possible with the latest technology. Whenever in doubt, we will add a note in our feature articles on the blog to indicate availability in either version.